Patient directed therapy control

ABSTRACT

A patient controls the delivery of therapy through volitional inputs that are detected by a biosignal within the brain. The volitional patient input may be directed towards performing a specific physical or mental activity, such as moving a muscle or performing a mathematical calculation. In one embodiment, a biosignal detection module monitors an electroencephalogram (EEG) signal from within the brain of the patient and determines whether the EEG signal includes the biosignal. In one embodiment, the biosignal detection module analyzes one or more frequency components of the EEG signal. In this manner, the patient may adjust therapy delivery by providing a volitional input that is detected by brain signals, wherein the volitional input may not require the interaction with another device, thereby eliminating the need for an external programmer to adjust therapy delivery. Example therapies include electrical stimulation, drug delivery, and delivery of sensory cues.

This application is a continuation of U.S. application Ser. No.15/012,646 by Panken et al., entitled “PATIENT DIRECTED THERAPYCONTROL,” filed Feb. 1, 2016 and issued as U.S. Pat. No. 10,258,798 onApr. 16, 2019, which is a continuation of U.S. application Ser. No.13/740,860 by Panken et al., entitled “PATIENT DIRECTED THERAPYCONTROL,” filed Jan. 14, 2013 and issued as U.S. Pat. No. 9,248,288 onFeb. 2, 2016, which is a continuation of U.S. application Ser. No.11/974,931 by Panken et al., entitled “PATIENT DIRECTED THERAPYCONTROL,” filed Oct. 16, 2007, and issued as U.S. Pat. No. 8,380,314 onFeb. 19, 2013, which claims the benefit of U.S. Provisional ApplicationNo. 60/975,372 by Denison et al., entitled “FREQUENCY SELECTIVEMONITORING OF PHYSIOLOGICAL SIGNALS,” and filed on Sep. 26, 2007. Theentire content of each of these applications is incorporated herein byreference.

TECHNICAL FIELD

The invention relates to medical devices and, more particularly, todevices that control therapy delivery.

BACKGROUND

Medical devices may be used to deliver therapy to patients to treat avariety of symptoms or conditions, such as chronic pain, tremor,Parkinson's disease, epilepsy, neuralgia, urinary or fecal incontinence,sexual dysfunction, obesity, or gastroparesis. A medical device maydeliver stimulation therapy via leads that include electrodes locatedproximate to the spinal cord, pelvic nerves, stomach, or within thebrain of a patient. In some cases, electrodes may be integrated with animplantable pulse generator, eliminating the need for leads. In somecases, a medical device may deliver a drug or another fluid to aspecific tissue site within the patient via a catheter attached to themedical device. Alternatively, a patient with a neurological disease maybe treated with external sensory cue. In any case, the medical device isused to provide treatment to the patient as needed in order in increasethe quality of life of the patient. The medical device may be implantedor located externally, depending upon the type of therapy and needs ofthe patient.

A clinician may program the medical device to effectively treat thepatient. For example, the clinician may define the therapy to bedelivered to a patient by selecting values for one or more programmabletherapy parameters. As one example, in the case of electricalstimulation, the clinician may select an amplitude, which may be acurrent or voltage amplitude, and pulse width for a stimulation waveformto be delivered to the patient, as well as a rate at which the pulsesare to be delivered to the patient. Programmable therapy parameters alsomay include electrode combinations and polarities. The clinician mayalso create multiple programs having various different therapy parametercombinations that the patient may use as desired in order to find themost effective therapy parameters to treat a condition.

At least in the case of a chronic therapy delivery system, the patientbegins to use the medical device for continued treatment during normaldaily activities after an initial programming session with theclinician. During treatment, the patient may need to adjust the therapyparameters in order to increase the efficacy of the therapy. Adjustmentsto therapy may include, for example, turning the therapy on and off,switching between therapy programs, and increasing or decreasing therapyamplitude. The patient uses an external programmer, e.g., a patientprogrammer, to communicate any desired adjustments to the medicaldevice. As an example, the external programmer may be a hand-heldcomputing device that includes a user interface that allows the user toselect certain adjustments to therapy. The patient may select theadjustments and the external programmer communicates the adjustments tothe medical device, resulting in an adjusted therapy. The patient maycontinue to use the external programmer throughout the duration oftherapy in order to retrain efficacious therapy.

SUMMARY

A patient may control an aspect of therapy delivery with volitionalinput, which is detected via biosignals within the brain. The biosignalsare generated in response to a volitional patient input and are notgenerated because of a symptom of the patient's condition. In this way,the patient may control therapy delivery via volitional thoughts.Therapy adjustment actions that may be taken in response to thedetection of the biosignal include initiating or deactivating therapydelivery, or increasing or decreasing a therapy parameter, such asamplitude of stimulation signals, pulse rate or frequency, in the caseof electrical stimulation. Therapy adjustment actions may also includeshifting between stored therapy programs.

The volitional patient input may not require the interaction with anexternal device. For example, the volitional input may includeperforming a specific physical or mental activity, such as moving aspecific muscle or muscle group or performing a mathematicalcalculation. In one embodiment, a biosignal detection module detects oneor more biosignals resulting from the volitional patient input bymonitoring an electroencephalogram (EEG) signal from within one or moreregions of the patient's brain, and determines whether the EEG signalincludes the biosignal. For example, the biosignal detection module oranother processor may analyze one or more predetermined frequency bandcomponents of the monitored EEG signal to determine whether the EEGsignal includes the biosignal.

Detection of a biosignal within the patient's brain that results from avolitional patient input allows a patient to control therapy without theuse of an external programmer. In this manner, therapy control is basedon brain signals, rather than interacting with a user interface of anexternal programmer. Example therapies include electrical stimulation,drug delivery, an externally or internally generated sensory cue, andany combination thereof. In addition, the system may support a learningmode to determine the biosignal. For example, one learning modecorrelates a monitored EEG signal with a volitional patient input. Acharacteristic of the EEG signal may be extracted from the monitored EEGsignal to generate the biosignal. In this way, the feedback for theclosed loop therapy adjustment may be customized to a particularpatient.

In one embodiment, the disclosure provides a method including detectingat least one biosignal from a brain of a patient that results from avolitional patient input, and controlling delivery of therapy to thepatient based on the biosignal.

In another embodiment, the disclosure provides a system comprising atherapy module to delivers therapy to a patient, a biosignal detectionmodule to detect at least one biosignal from a brain of a patient thatresults from a volitional patient input, and a processor to controls thetherapy device based on the detection of the biosignal.

In another embodiment, the disclosure is directed to a system thatincludes a sensing module configured to sense an electroencephalogram(EEG) signal of a patient, and a processor to determine whether the EEGsignal includes a biosignal. The biosignal is based on a volitionalpatient input, wherein the processor generates a control signal tocontrol a therapy module if the EEG signal includes the biosignal.

The disclosure provides one or more advantages. For example, the therapysystems eliminate the need for an external programmer to adjust therapy,which allows the patient to adjust therapy in situations where use of aprogrammer may not be possible or suggested. Example situations includebathing, swimming, driving, or any situation in which the patient maynot be able to carry a programmer or the patient does not have a freehand.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram illustrating an embodiment of a deepbrain stimulation system that includes a biosignal detection module todetect a volitional patient input to control therapy.

FIG. 2A is a conceptual diagram illustrating an embodiment of a spinalcord stimulation system with a biosignal detection module used by thepatient to control therapy.

FIG. 2B is a conceptual diagram illustrating another embodiment of aspinal cord stimulation system that includes an external biosignaldetection module.

FIG. 3 is a conceptual diagram illustrating an embodiment of a sensorycue system that includes a biosignal detection module.

FIG. 4 is functional block diagram illustrating components of anembodiment of an electrical stimulator.

FIG. 5 is functional block diagram illustrating components of anembodiment of a drug pump.

FIG. 6 is functional block diagram illustrating components of anexemplary sensory cue device.

FIG. 7 is a functional block diagram illustrating components ofbiosignal detection module that is separate from a therapy module.

FIG. 8 is functional block diagram illustrating components of anembodiment of an external programmer.

FIGS. 9A and 9B are flow diagrams illustrating embodiments of techniquesfor adjusting therapy according to detected biosignals from the patient.

FIGS. 10A and 10B are a flow diagram illustrating embodiments oftechniques that may be employed to control a therapy device based on anEEG signal.

FIG. 11 is an example electrical signal received by the biosignaldetection module that indicates when a patient closes and opens hiseyes.

FIG. 12 is an embodiment of a programmer with a user interface thatallows the programmer to learn and match biosignals to patientactivities.

FIG. 13 is a flow diagram illustrating an embodiment of a technique thatmay be employed by the programmer of FIG. 12 to correlate biosignalswith volitional patient activities.

FIG. 14 is a flow diagram illustrating an embodiment of a technique forassociating a volitional patient input with an EEG signalcharacteristic.

FIG. 15 is a block diagram illustrating an exemplary frequency selectivesignal monitor that includes a chopper-stabilized superheterodyneamplifier and a signal analysis unit.

FIG. 16 is a block diagram illustrating a portion of an exemplarychopper-stabilized superheterodyne amplifier for use within thefrequency selective signal monitor from FIG. 15.

FIGS. 17A-17D are graphs illustrating the frequency components of asignal at various stages within the superheterodyne amplifier of FIG.16.

FIG. 18 is a block diagram illustrating a portion of an exemplarychopper-stabilized superheterodyne amplifier with in-phase andquadrature signal paths for use within a frequency selective signalmonitor.

FIG. 19 is a circuit diagram illustrating a chopper-stabilized mixeramplifier suitable for use within the frequency selective signal monitorof FIG. 15.

FIG. 20 is a circuit diagram illustrating a chopper-stabilized,superheterodyne instrumentation amplifier with differential inputs.

DETAILED DESCRIPTION

Medical devices are useful for treating or otherwise control variouspatient conditions or disorders. In some cases, medical devices may beused to deliver therapy to patients having conditions or disorders thatcannot be effectively treated with diet, exercise, lifestyle changes,orally ingested pharmaceuticals, or any other treatment regimen. Medicaldevices may be configured to deliver therapies such as electricalstimulation, drug delivery or internally or externally generated sensorycues (or “stimuli”) that reduce or eliminate the patient condition ordisorder. Depending upon the type of therapy delivered by the medicaldevice, the medical device may be implanted in the patient for chronictherapy delivery (e.g., longer than a temporary, trial basis).

In some cases, a medical device may be programmed with different therapyparameters. The therapy parameters may be selected to address aparticular patient's condition during the initial stages of therapyimplementation, as well as during follow-up visits to a clinician'soffice. In some cases, the clinician may create multiple programs thateach have different therapy parameters selected by the clinician. Theseprograms may also be referred to as therapy “parameter sets.” During atrial stage, the patient may evaluate the different therapy programs toidentify the therapy programs that provide the most efficacioustreatment relative to the other tested programs.

Based on the trial stage or other considerations, the clinician and/orpatient may select one or more therapy programs for use by the medicaldevice during chronic therapy delivery. In some cases, the patient maybe given the freedom to select one or more therapy programs with whichto delivery therapy or to increase or decrease therapy parameters asneeded to increase the efficacy of therapy. For example, if anelectrical stimulator is implanted within the patient, the patient mayincrease or decrease a stimulation parameter, such as the current orvoltage amplitude of the stimulation, within a predetermined range. Theclinician or the manufacturer of the electrical stimulator may selectthe predetermined range. In the case of electrical stimulation therapy,the range is typically selected such that the electrical stimulationdoes not harm the patient.

In the therapy systems described herein, a patient may adjust one ormore aspects of therapy via a volitional patient input that is detectedvia a biosignal within the brain. In one embodiment, the biosignal isgenerated within the brain in response to a volitional thought, such asa thought relating to a particular muscle movement (e.g., facialtwitching, moving a finger, etc.). Thus, the patient may provide theinput by moving a muscle, performing a particular calculation within hishead, or any other volitional thought that produces a detectableelectrical signal within the brain. The volitional patient input isassociated with a particular therapy adjustment action, such asinitiating therapy, deactivating therapy or increasing or decreasing atherapy parameter.

The one or more biosignals that are used to detect the volitionalpatient input may be selected to be unique, i.e., differentiated fromother brain signals that are unrelated to the volitional patient input,in order to minimize the number of false positives. A false positive maybe, for example, detecting the biosignal when the patient did actuallyprovide the volitional patient input. In such a case, the biosignal maybe incorrectly detected, e.g., because of its similarity to anotherbrain signal unrelated to the volitional patient input.

The therapy systems described herein include a biosignal detectionmodule that detects the biosignal generated within the brain based onthe patient input. The biosignal detection module provides feedback to atherapy device (or a “therapy module”), which adjusts therapyaccordingly. In this way, the systems described herein eliminate theneed for a patient to interact with an external programming device inorder to adjust therapy. However, in some embodiments, the biosignalfeedback system described herein may be used to control therapy inaddition to an external programmer.

The biosignal detection module may employ an algorithm to suppress falsepositives, i.e., the adjustment of therapy in response to a brain signalthat is not the biosignal indicative of the patient input. For example,in addition to selecting a unique biosignal, the biosignal detectionmodule may implement an algorithm that identifies particular attributesof the biosignal (e.g., certain frequency characteristics of thebiosignal) that are unique to the patient input. As another example, thebiosignal detection module may monitor the characteristics of thebiosignal in more than one frequency band, and correlate a particularpattern in the power of the brain signal within two or more frequencybands in order to determine whether the brain signal is indicative ofthe volitional patient input. As another example, the volitional patientinput may include a pattern of volitional actions or thoughts thatgenerate a specific pattern of brain signals or a brain signal includingspecific attributes that may be identified by the biosignal detectionmodule. The specific attributes may include, for example, a pattern inthe amplitude waveform of a bioelectrical brain signal, or a pattern orbehavior of the frequency characteristics of the bioelectrical brainsignal, and so forth.

In some embodiments, a biosignal detection module acquires abioelectrical signal from within one or more regions of a patient'sbrain using implanted or external electrodes. The bioelectrical signalmay include an electroencephalogram (EEG) signal, electromyogram (EMG)signal, electrocorticogram (ECoG) signal, field potentials within themotor cortex or other regions of the brain, or combinations thereof.

In one embodiment, the biosignal detection module acquires an EEG signalfrom within one or more regions of a patient's brain using one or moreelectrodes placed on the head or implanted within the patient. An EEGsignal indicates the electrical activity within a brain of a patient.The biosignal detection module may be implanted within the patient ormay be carried external to the patient. A processor within the biosignalsensing module, therapy module or another part of the therapy systemdetermines whether the monitored EEG signal includes the biosignal viamany suitable techniques. As described in further detail below, in oneembodiment, a processor processes the EEG signal by tuning into, orextracting, a specific frequency band from the EEG signal that containsinformation pertinent to a volitional patient input. The biosignal maythen be a component of the EEG signal within the extracted frequencyband.

The therapy systems described herein do not directly alter therapy basedupon symptoms of the patient's condition or disease. Rather, the therapysystems implement a biosignal that provides feedback to a therapymodule, where the biosignal is nonsymptomatic. That is, the biosignal isunrelated to a condition of the patient's disease. Furthermore, thebiosignal results from a volitional patient input, rather than anincidental electrical signal within the patient's brain that the patientdid not voluntarily or intentionally generate. Thus, the detection of avolitional patient input that indicates a desired to therapy adjustmentaction differs from involuntary neuronal activity that may be caused bythe patient's condition (e.g., a tremor or a seizure). In someembodiments, symptomatic physiological changes may be detected by thesystem and used as feedback to increase therapy efficacy. However, thesesymptomatic changes in the brain are not the biosignals detected by thebiosignal detection module that allow the patient direct control overtherapy. Instead, the biosignal detection module detects a particularbiosignal within the patient's brain that results from a volitionalinput, thereby allowing the patient to control one or more aspects oftherapy by voluntarily causing a detectable physiological change withinthe brain.

The patient 12 may wish to adjust therapy for many different reasons.For example, if the therapy system is implemented to control pain,patient may initiate therapy delivery or increase/decrease therapydelivery parameters as the patient's pain level changes. As anotherexample, if therapy system 10 is used to treat or control seizures, andpatient 12 sees an aura or another indication that a seizure is likelyto occur, patient 12 may provide volitional input to initiate orincrease therapy delivery in an attempt to stop the onset of theseizure.

In some embodiments, once the therapy system is implemented in thepatient, the therapy system may be programmed to link biosignals withinthe brain to specific volitional patient inputs with specific patientactivities, from which the type of therapy adjustment may be determined.In other embodiments, the therapy system may be programmed to linkbiosignals within the brain to specific therapy adjustment actions. Asdescribed in further detail below, the biosignals may be determinedduring a learning mode, and a clinician or a computing device mayassociate certain biosignals with respective therapy adjustment actions.In one embodiment, a therapy system may be preprogrammed to performcertain therapy adjustments upon detecting biosignals for certainactions. For example, if the patient wishes to cease therapy delivery,the patient may produce a volitional thought directed to moving his eyesdown. In other embodiments, the therapy system may combine the biosignaldetection with a secondary input means, such as tapping anaccelerometer, or a combination of biosignals prior to implementing theindicated therapy adjustment action.

In some cases, the patient may produce biosignals in a particularpattern generated from a sequence of voluntary thought in order tominimize unwanted changes in therapy from biosignals detected duringnormal daily activity. Example sequences may involve multiple eyemovements, facial expressions, limb movements, and any other thoughtsequences that are detectable by the biosignal sensing module.

The learning mode is not only useful during the initial programming ofthe therapy system, but also throughout implementation of the chronictherapy system. For example, after the initial programming of thetherapy system, the patient may change certain correlations between aparticular biosignal and an associated therapy action, remove acorrelated activity that is commonly used by the patient or add a newcorrelation between a biosignal and a therapy action. In some cases, theclinician may prompt the patient to reenter the learning mode after achange in therapy is produced or because of a progression in thepatient's disease.

The patient may realize many advantages when controlling therapy withbiosignals that are based on volitional thought. For example, thetherapy system described herein eliminates the need for the patient tocarry an external programmer throughout the day in order to take therapyactions, such as changing programs, increasing amplitude, and turningthe therapy on and off. Carrying the programmer may be burdensome on thepatient, and may be an indiscreet mechanism for adjusting therapy, whichmay cause social discomfort to the patient. In addition, the patient maynot be able to use the external programmer during certain activitiessuch as swimming, showering, driving, exercising, or when the patient'shands are occupied. In this manner, a therapy systems in whichbiosignals within a patient's brain provide input to adjust therapy mayprovide additional safety and security to the patient by permitting thepatient to adjust therapy in many circumstances in which an externalprogrammer may not be practical.

Biosignal detection may also be beneficial for patients unable orunwilling to use an external programmer. For example, the therapysystems described herein may be useful for blind patients, who may findit difficult to manipulate an external programmer. The therapy systemsdescribed herein may also be useful for elderly patients, who may findit difficult to master the use of the external programmer due to arelative complicated user interface. In addition, biosignal detectionmay allow patients with movement disorders, such as Parkinson's disease,to initiate therapy when a motion impairment condition (e.g., tremor)may be too severe to provide an input to an external programmer.Additional advantages are also provided by the biosignal receptiontherapy system described herein, depending upon the embodimentimplemented to the patient.

The therapy system described herein may receive biosignals to controlany type of therapy. Example therapies include, but are not limited to,pain therapy, spinal cord stimulation (SCS), deep brain stimulation(DBS), peripheral nerve stimulation (PNS), peripheral nerve fieldstimulation (PNFS), incontinence therapy, gastric stimulation, andpelvic floor stimulation. These and other therapies may be directedtoward treating conditions such as chronic pain, incontinence, sexualdysfunction, obesity, migraine headaches, Parkinson's disease,depression, epilepsy, seizures, or any other neurological disease.Additional conditions and diseases may also be treated by detectingbiosignals to control delivery of a therapy. While therapy describedherein is preferably directed to human patients, the therapy may beapplied to non-human patients as well.

FIG. 1 is a conceptual diagram illustrating an example DBS system 10,which includes implantable medical device (IMD) 18, lead extension 22,leads 24A and 24B, and electrode array 25. IMD 18 includes a therapymodule that delivers electrical stimulation therapy to patient 12 vialeads 24A and 24B, as well as a biosignal detection module that detectsone or more biosignals indicative of one or more volitional patientinputs relating to therapy adjustment actions. As described in furtherdetail below, the biosignal detection module provides feedback to thetherapy module to control one or more aspects of therapy delivery.

IMD 18 is implanted in patient 12. Implanted lead extension 22 iscoupled to IMD 18 via connector 20. Lead extension 22 traverses from theimplant site of IMD 18 within a chest cavity of patient 12, and alongthe neck of patient 12 to cranium 14 of patient 12 to access brain 16.Leads 24A and 24B (collectively “leads 24”) are implanted within theright and left hemispheres, respectively, of patient 12 in order deliverelectrical stimulation to one or more regions of brain 16, which may beselected based on the patient condition or disorder controlled by DBSsystem 10. Electrode array 25 includes a plurality of electrodes 26,which are carried by lead 28, to detect biosignals within brain 16 thatresult from a volitional patient thought. External programmer 30wireless communicates with IMD 18 as needed to provide or retrievetherapy information. While patient 12 is generally referred to as ahuman patient, other mammalian or non-mammalian patients are alsocontemplated.

Although leads 24 are shown in FIG. 1 as being coupled to a common leadextension 22, in other embodiments, leads 24 may be coupled to IMD 18via separate lead extensions or directly to the therapy module. Leads 24may deliver electrical stimulation to treat any number of neurologicaldisorders or diseases. Example neurological disorders may includedepression, dementia, obsessive-compulsive disorder, and movementdisorders, such as Parkinson's disease, spasticity, and epilepsy. DBS isalso useful for treating other patient conditions, such as migraines andobesity.

Leads 24 may be implanted within a desired location of brain 16 throughrespective holes in cranium 14. Leads 24 may be placed at any locationwithin brain 16 such that the electrodes of the leads are capable ofproviding electrical stimulation to targeted tissue during treatment.Electrical stimulation generated from the signal generator (not shown)within the therapy module of IMD 18 may be configured to treat a varietyof disorders and conditions. Example locations for leads 24 within brain16 may include the pedunculopontine nucleus (PPN), thalamus, basalganglia structures (e.g., globus pallidus, substantia nigra, subthalamicnucleus), zona inserta, fiber tracts, lenticular fasciculus (andbranches thereof), ansa lenticularis, and/or the Field of Forel(thalamic fasciculus). In the case of migraines, leads 24 may beimplanted to provide stimulation to the visual cortex of brain 16 inorder to reduce or eliminate migraine headaches afflicting patient 12.In addition, as described in further detail below, electrode array 25 orsensing electrodes of leads 24 may be positioned to monitor an EEG fromwithin the visual cortex of brain. In the case of obesity orcompulsive-eating disorders, leads 24 may be placed to providestimulation to provide negative feedback to patient 12, e.g.,stimulating a sensory cortex of brain 16 to cause patient 12 to believefood tastes bad. However, the target therapy delivery site may dependupon the patient condition or disorder being treated.

The electrodes of leads 24 are shown as ring electrodes. Ring electrodesare commonly used in DBS applications because they are simple to programand are capable of delivering an electrical field to any tissue adjacentto leads 24. In other embodiments, the electrodes of leads 24 may havedifferent configurations. For examples, the electrodes of leads 24 mayhave a complex electrode array geometry that is capable of producingshaped electrical fields. The complex electrode array geometry mayinclude multiple electrodes (e.g., partial ring or segmented electrodes)around the perimeter of each lead 24, rather than one ring electrode. Inthis manner, electrical stimulation may be directed to a specificdirection from leads 24 to enhance therapy efficacy and reduce possibleadverse side effects from stimulating a large volume of tissue. In someembodiments, a housing of IMD 18 may include one or more stimulationand/or sensing electrodes. In alternative examples, leads 24 may be haveshapes other than elongated cylinders as shown in FIG. 1. For example,leads 24 may be paddle leads, spherical leads, bendable leads, or anyother type of shape effective in treating patient 12.

IMD 18 includes a therapy module that generates the electricalstimulation delivered to patient 12 via leads 24. A signal generator(not shown), within IMD 18 produces the stimulation in the mannerdefined by the therapy parameters selected by the clinician and/orpatient 12. Generally the signal generator is configured to produceelectrical pulses to treat patient 12. However, the signal generator ofIMD 18 may be configured to generate a continuous wave signal, e.g., asine wave or triangle wave. In either case, IMD 18 generates theelectrical stimulation therapy for DBS according to therapy parametersselected at that given time in therapy.

In the embodiment shown in FIG. 1, IMD 18 generates the electricalstimulation according to one or more therapy parameters, which may bearranged in a therapy program (or a parameter set). The therapy programincludes a value for a number of parameters that define the stimulation.For example, the therapy parameters may include voltage or current pulseamplitudes, pulse widths, pulse rates, pulse frequencies, electrodecombinations, and the like. IMD 18 may store a plurality of programs.During a trial stage in which IMD 18 is evaluated to determine whetherIMD 18 provides efficacious therapy to patient 12, the stored programsmay be tested and evaluated for efficacy. During chronic therapy inwhich IMD 18 is implanted within patient 12 for delivery of therapy on anon-temporary basis, patient 12 may select the programs for deliveringtherapy. For example, the different programs may provide moreefficacious therapy during different activities, different times of theday, and so forth. Thus, patient 12 may modify the value of one or moreparameters within a single given program or switch between programs inorder to alter the efficacy of the therapy as perceived by patient 12.

IMD 18 may include a memory to store one or more therapy programs,instructions defining the extent to which patient 12 may adjust therapyparameters, switch between programs, or undertake other therapyadjustments. Patient 12 may generate additional programs for use by IMD18 via external programmer 30 at any time during therapy or asdesignated by the clinician. Patient 12 may also generate additionaltherapy programs by adjusting the one or more therapy parameters withvolitional inputs that are detected via biosignals within brain 16. Inparticular, a biosignal detection module within IMD 18 detects thebiosignals via electrode array 25. If patient 12 modifies a therapyprogram, patient 12 may provide input to therapy system 10 that causesthe therapy module within IMD 18 to save the parameters as a new therapyprogram for later use.

Generally, IMD 18 is constructed of a biocompatible material thatresists corrosion and degradation from bodily fluids. IMD 18 may beimplanted within a subcutaneous pocket close to the stimulation site.Although IMD 18 is implanted within a chest cavity of patient 12 in theembodiment shown in FIG. 1, in other embodiments, IMD 18 may beimplanted within cranium 14. While IMD 18 is shown as implanted withinpatient 12 in FIG. 1, in other embodiments, IMD 18 may be locatedexternal to the patient. For example, IMD 18 may be a trial stimulatorelectrically coupled to leads 24 via a percutaneous lead during a trialperiod. If the trial stimulator indicates therapy system 10 provideseffective treatment to patient 12, the clinician may implant a chronicstimulator within patient 12 for long term treatment.

Electrode array 25 is implanted within cranium 14 of patient 12 andpositioned to detect an electroencephalogram (EEG) signal within aparticular region of patient's brain 16, which may depend upon the typeof volitional patient input that generates the biosignal. Electrodearray 25 may be surgically implanted under the dura matter of brain 16or within the cerebral cortex of brain 16 via a burr hole in a skull ofpatient 12. In some cases, electrodes 26 implanted closer to the targetregion of brain 16 may help generate an EEG signal that provides moreuseful information than an EEG generated via a surface electrode arraybecause of the proximity to brain 16. The EEG signal that is generatedfrom implanted electrode array may also be referred to as an ECoG.

Electrode array 25 may be positioned to detect an EEG signal within amotor cortex, a sensory motor strip, the visual cortex (e.g., theoccipital cortex), cerebellum or the basal ganglia of brain 16.Volitional patient inputs in the form of muscle movement, e.g., movementof a finger, arm, leg or facial muscle, may generate detectable changes(i.e., detectable biosignal) in the EEG signal from within the motorcortex. Volitional patient input in the form of eye movement, e.g.,moving eyes in certain directions, opening eyes or closing eyes, maygenerate a detectable biosignal in the occipital cortex of brain 16.

Electrode array 25 is coupled to IMD 18 via lead extension 22 or anotherlead extension. In other embodiments, electrode array 25 may communicatewith IMD 18 via wireless telemetry, rather than a wired connection asshown in FIG. 1. For example, electrode array 25 may be integrated intoa separate biosignal detection module that includes a housing thatincludes a processor, memory, telemetry interface, battery, and anyother component necessary for the sensing signal to transfer data. Datamay be transferred to IMD 18 and/or programmer 30. An embodimentincluding a separate biosignal detection module is shown and describedwith reference to FIG. 2.

Electrode array 25 includes lead 28 that is coupled to electrodes 26.Electrodes 26 are shown as implanted under the skin covering cranium 14,but the electrodes may be implanted between cranium 14 and brain 16(e.g., under the dura), within brain 16 (e.g., “deep brain”), orexternally over the skin in alternative embodiments. Electrodes 26 areconfigured to receive electrical signals produced from neuronal activitywithin brain 16. These signals may make up EEG and, accordingly arereferred to as “EEG signals.” In any case, electrodes 26 are positionedaround brain 16 in order to receive signals emanating from targetedlocations within the brain. The targeted locations may be thoselocations in which the patient thought relating to the volitionalpatient input occurs.

The biosignal detection module within IMD 18 is configured to monitor anEEG from within a region of brain 16 and determine whether the EEGsignal includes the biosignal that is generated when patient 12 providesthe volitional input relating to the therapy adjustment action. While anEEG signal within the motor cortex is primarily referred to throughoutthe remainder of the application, in other embodiments, therapy system10 may detect a biosignal within other regions of brain 16. The motorcortex is defined by regions within the cerebral cortex of brain 16 thatare involved in the planning, control, and execution of voluntary motorfunctions, such as walking and lifting objects. Typically, differentregions of the motor cortex control different muscles. For example,different “motor points” within the motor cortex may control themovement of the arms, trunk, and legs of patient. Accordingly,electrodes array 25 may be positioned to sense the EEG signals withinparticular regions of the motor cortex, e.g., at a motor point that isassociated with the movement of the arms, depending on the type ofvolitional patient input system 10 is configured to recognize as atherapy adjustment input.

EEG is typically a measure of voltage differences between differentparts of brain 16, and, accordingly, electrode array 25 may include twoor more electrodes. The sensing module within IMD 18 may then measurethe voltage across at least two electrodes of array 25. Although fourelectrodes are shown in FIG. 1, in other embodiments, electrode array 25may include any suitable number of electrodes. One or more of theelectrodes 26 may act as a reference electrode for determining thevoltage difference of one or more regions of brain 16. Lead 28 couplingelectrodes 26 to IMD 18 may, therefore, include a separate, electricallyisolated conductor for each electrode 26.

Electrodes 26 of array 25 may be positioned to detect EEG signals fromone or more select regions within brain 16, which may depend upon thetype of volitional patient thoughts that are used as an input to controltherapy. Electrode array 25 may only include those electrodes 26necessary to the operation of system 10 to minimize the number ofdevices placed on or implanted within patient 12. Electrodes 26 may beplaced to detect biosignals within more than one region of brain 16 iftherapy system 10 is configured to recognize more than one biosignal tocontrol therapy.

In other embodiments, electrode array 25 may be carried by at least oneof leads 24A and/or 24B instead of or in addition to electrodes 26 thatare separate from leads 24A and 24B. This configuration of electrodearray 25 may be useful when the relevant biosignals when are generatednear the same region of brain 16 as the target therapy delivery site.

Programmer 30 is an external computing device that the user, i.e., theclinician and/or patient 12, uses to communicate with IMD 18. Forexample, programmer 30 may be a clinician programmer that the clinicianuses to communicate with IMD 18. Alternatively, programmer 30 may be apatient programmer that allows patient 12 to view and modify therapyparameters. The clinician programmer may include more programmingfeature than the patient programmer. In other words, more complex orsensitive tasks may only be allowed by the clinician programmer toprevent the untrained patient from making undesired changes to IMD 18.

Programmer 30 may be a hand-held computing device with a displayviewable by the user and a user input mechanism that can be used toprovide input to programmer 30. For example, programmer 30 may include asmall display screen (e.g., a liquid crystal display or a light emittingdiode display) that provides information to the user. In addition,programmer 30 may include a keypad, buttons, a peripheral pointingdevice or another input mechanism that allows the user to navigatethrough the user interface of programmer 30 and provide input. Ifprogrammer 18 includes buttons and a keypad, the buttons may bededicated to performing a certain function, i.e., a power button, or thebuttons and the keypad may be soft keys that change in functiondepending upon the section of the user interface currently viewed by theuser. Alternatively, the screen (not shown) of programmer 30 may be atouch screen that allows the user to provide input directly to the userinterface shown on the display. The user may use a stylus or theirfinger to provide input to the display. An embodiment of programmer 30is described below with reference to FIGS. 8 and 12.

In other embodiments, programmer 30 may be a larger workstation or aseparate application within another multi-function device. For example,the multi-function device may be a cellular phone or personal digitalassistant that can be configured to an application to simulateprogrammer 30. Alternatively, a notebook computer, tablet computer, orother personal computer may enter an application to become programmer 30with a wireless adapter connected to the personal computer forcommunicating with IMD 18.

When programmer 30 is configured for use by the clinician, programmer 30may be used to transmit initial programming information to IMD 18. Thisinitial information may include system 10 hardware information such asthe type of leads 24 and the electrode arrangement, the position ofleads 24 within brain 16, the configuration of electrode array 25,initial programs having therapy parameters, and any other informationthe clinician desires to program into IMD 18. Programmer 30 may also becapable of completing any functional tests (e.g., measuring theimpedance of electrodes 26 or the electrodes of leads 24A and 24B) theclinician desires to complete before starting therapy and sendingpatient 12 home.

The clinician also uses programmer 30 to program IMD 18 with initialstimulation programs, defined as programs that define the therapydelivered by IMD 18. During a programming session, the clinician maydetermine one or more therapy programs that may provide effectivetherapy to patient 12. Patient 12 may provide feedback to the clinicianas to the efficacy of the specific program being evaluated. Once theclinician has identified one or more programs that may be beneficial topatient 12, patient 12 may continue the evaluation process and determinewhich program best alleviates the condition of patient 12. Programmer 30may assist the clinician in the creation/identification of therapyprograms by providing a methodical system of identifying potentiallybeneficial therapy parameters.

As described in further detail below, a clinician may also set or modifythe parameters of the biosignal detection module within IMD 18 with theaid of programmer 30 during an initial programming session or at a latertime. For example, programmer 30 may help associate a biosignal that isgenerated within brain 16 with one or more volitional patient inputs(e.g., movement of a particular muscle). Programmer 30 may also helpcorrelate a biosignal with a particular therapy activity (e.g., a pulseamplitude adjustment) or modify the correlation between a particularbiosignal and a therapy activity. In addition, programmer 30 may helpthe clinician identify which electrodes 26 provide the most usefuldetection of the biosignals, because some electrodes 26 may acquire abetter EEG signals than other electrodes 26.

Programmer 30 may also be configured for use by patient 12. Whenconfigured as the patient programmer, programmer 30 may have limitedfunctionality in order to prevent patient 12 from altering criticalfunctions or applications that may be detrimental to patient 12. In thismanner, programmer 30 may only allow patient 12 to adjust certaintherapy parameters or set an available range for a particular therapyparameter. Programmer 30 may also include a learning mode thatautomatically correlates biosignals detected by the biosignal detectionmodule within IMD 18 to activities of patient 12 or desired therapyadjustments. Programmer 30 may also provide an indication to patient 12when therapy is being delivered, when biosignals have triggered a changein therapy, or when IMD 18 or when the power source within programmer 30or IMD 18 need to be replaced or recharged.

Whether programmer 30 is configured for clinician or patient use,programmer 30 may communicate to IMD 18 or any other computing devicevia wireless communication. Programmer 30, for example, may communicatevia wireless communication with IMD 18 using radio frequency (RF)telemetry techniques known in the art. Programmer 30 may alsocommunicate with another programmer or computing device via a wired orwireless connection using any of a variety of local wirelesscommunication techniques, such as RF communication according to the802.11 or Bluetooth specification sets, infrared communication accordingto the IRDA specification set, or other standard or proprietarytelemetry protocols. Programmer 30 may also communicate with anotherprogramming or computing device via exchange of removable media, such asmagnetic or optical disks, or memory cards or sticks. Further,programmer 30 may communicate with IMD 18 and other another programmervia remote telemetry techniques known in the art, communicating via alocal area network (LAN), wide area network (WAN), public switchedtelephone network (PSTN), or cellular telephone network, for example.

Therapy system 10 may be implemented to provide chronic stimulationtherapy to patient 12 over the course of several months or years.However, system 10 may also be employed on a trial basis to evaluatetherapy before committing to full implantation. If implementedtemporarily, some components of system 10 may not be implanted withinpatient 12. For example, patient 12 have be fitted with an externalmedical device, rather than IMD 18 that is coupled to percutaneousleads. In addition, electrode array 25 may be placed over the scalp ofpatient 12 to monitor the relevant EEG signals, and coupled to theexternal medical device or a separate biosignal detection module.

In some embodiments of the therapy systems described herein, the therapysystem may provide feedback to patient 12 to indicate that thevolitional input was received. For example, the sensory cortex of brain16 may be stimulated to provide the sensation of a visible light. Otherforms of sensory feedback are also possible, such as an audible sound ora somatosensory cue. In some embodiments, programmer 30 may include afeedback mechanism, such an LED, another display or a sound generator,which indicates that the therapy system received the volitional patientinput and that the appropriate therapy adjustment action was taken.

FIG. 2A is a conceptual diagram illustrating an example spinal cordstimulation (SCS) system 32, which includes IMD 36 configured to deliverstimulation to spinal cord 34, leads 38A and 38B (collectively “leads38”) coupled to IMD 36, electrode array 25 positioned to detect an EEGsignal within a motor cortex of brain 16 of patient 12, and biosignaldetection module 39. SCS system 32 is substantially similar to therapysystem 10 of FIG. 1. However, IMD 36 is configured to deliver electricalstimulation therapy to spinal cord 34 of patient 12 and biosignaldetection module 39 is separate from IMD 36 and implanted within cranium14.

Leads 38 are implanted adjacent to spinal cord 34 such that electrodes(not shown) of each of leads 38 are capable of delivering electricalstimulation to the desired area of spinal cord 34. Although leads 38 arepositioned to achieve bilateral stimulation of spinal cord 34, in otherembodiments, leads 38 may be positioned to achieve unilateralstimulation.

SCS therapy may be used, for example, to reduce pain experienced bypatient 12. Although IMD 36 is described for purposes of illustration,various embodiments of this disclosure also may be applicable toexternal therapy modules that reside outside the patient's body, anddeliver stimulation therapy using one of more implanted leads deployedvia a percutaneous port. For example, the functions of IMD 36 may becombined with the functions of programmer 30 and implemented in a singleexternal device that provides stimulation therapy. In other embodiments,leads 38 may be placed to deliver stimulation to other target siteswithin patient 12, where the target sites depend on the patientcondition treated by therapy system 32. Also, in some embodiments, IMD36 may be a leadless microstimulator in which electrodes are carried onor near an electrical stimulator housing.

Just as with IMD 18 of FIG. 1, IMD 36 delivers electrical stimulationtherapy to patient 12 via electrodes of leads 38. IMD 36 may deliverstimulation therapy to patient 12 according to a program groupcontaining plurality of programs for a single symptom area, such as anumber of leg pain programs. The plurality of programs for the singlearea may be a part of a program group for therapy. In addition, multiplegroups may target similar areas of patient 12. IMD 36 may have differentprogram parameters for each of the leg pain programs based on a positionof patient 12, an activity rate of patient 12, or other patientparameters. Programs in a group may be delivered simultaneously or on atime-interleaved basis, either in an overlapping or non-overlappingmanner.

Patient 12 may adjust the SCS therapy delivered by IMD 36 by providing avolitional patient input that results in a biosignal within brain 16that is detectable by biosignal detection module 39. Just as withtherapy system 10 of FIG. 1, the volitional patient input may be avolitional thought, such as thoughts relating to volitional actions.Examples of volitional actions include, but not limited to, eyeblinking, facial muscle twitches, finger movements, or any other thoughtthat is manifested in an electrical signal from brain 16. In addition,biosignals detectable by biosignal detection module 39 may be indicativeof volitional patient thoughts that do not result in physical movementor even directed to movement. For example, the mere thought of moving afinger may generate a detectable EEG signal within the motor cortex ofbrain 16. As another example, patient 12 may perform a particularmathematical calculation or perform another focused task that generatesa detectable EEG signal within another region of brain 16. In thismanner, patient 12 may adjust stimulation therapy without physicallyinteracting with programmer 30.

Biosignal detection module 39 and electrode array 25 are implantedwithin a cranium 14 of patient 12. Biosignal detection module 39 isdescribed in further detail below with reference to FIG. 7. In general,the embodiment of biosignal detection module 39 shown in FIG. 2Awirelessly communicates with IMD 36 using any suitable wirelesscommunication technique, such as RF communication techniques. In oneembodiment, biosignal detection module 39 includes a processor thatprocesses the EEG signals monitored via electrode array 25 anddetermines when the biosignal is detected. Upon detecting the biosignalthat is indicative of the patient input, the processor within biosignaldetection module 39 may generate a therapy adjustment indication that istransmitted IMD 36 via wireless telemetry techniques. In response toreceiving the therapy adjustment indication, IMD 36 may adjust therapyaccordingly. Different therapy adjustment indications may be generated.For example, biosignal detection module 39 may generate a therapyadjustment indication that initiates therapy, another indication thatdeactivates therapy, and other indications that increment or decrement atherapy parameter (e.g., pulse rate).

In another embodiment, biosignal detection module 39 monitors the EEGsignal and transmits the EEG signal to IMD 36, which includes aprocessor to determine when the biosignal is detected. In otherembodiments of SCS system 32, biosignal detection module 39 may beintegrated in a common housing with IMD 36, and electrode array 25 maybe coupled to IMD 36 via a wired connection, such as a lead or leadextension that tunneled to IMD 36.

System 32 is not limited to the combination of leads 38 shown in FIG.2A. For example, system 10 may include only a single lead or more thantwo leads implanted proximate to spinal cord 34. In addition, thedisclosure further contemplates the use of one or more leadlessmicrostimulators carrying or integrating electrodes in the stimulatorhousing. Furthermore, the invention is not limited to the delivery ofSCS therapy. For example, one or more leads 38 may extend from IMD 36 tothe brain (not shown) of patient 12. As further examples, one or moreleads 38 may be implanted proximate to the pelvic nerves (not shown) orstomach (not shown), and IMD 36 may deliver stimulation therapy to treatincontinence, obesity, gastroparesis. IMD 36 may also be used forperipheral nerve stimulation. In some embodiments, IMD 36 is configuredto deliver functional electrical stimulation (FES) or transcutaneouselectrical stimulation (TENS) of a muscle or muscle group of patient 12in order to help initiate movement or help patient 12 control movementof a limb or other body part. Alternatively, IMD 36 may take the form ofone or more microstimulators implanted within a muscle of patient 12.

Leads 38 may be any type of leads commonly used in SCS therapy. Forexample, leads 38 may be paddle leads or leads with ring electrodes.Alternatively, leads 38 may have a complex electrode array geometry withmultiple electrodes (e.g., partial ring or segmented electrodes) aroundthe perimeter of each lead. In this manner, the clinician may select thespecific electrodes necessary for therapy without stimulatingunnecessary tissue. The complex electrode array geometry of leads 38 mayalso be described as partial ring electrodes when IMD 36 is capable ofdelivering electrical stimulation to specific sides of leads 38. In thismanner, therapy parameters may be selected to offset any inaccurateimplantation of the leads or lead migration over time.

FIG. 2B is a conceptual diagram illustrating another embodiment of anSCS system 40, which includes IMD 36 configured to deliver stimulationto spinal cord 34, leads 38 coupled to IMD 36, and external biosignaldetection module 42 coupled to surface electrode array 44. Rather thanan implanted biosignal detection module 39 and implanted electrode array25, as in the SCS system 32 of FIG. 2A, SCS system 40 detects therelevant biosignals indicative of a therapy adjustment command viaexternal biosignal detection module 42 coupled to surface electrodearray 44. Biosignal detection module 42 is substantially similar tobiosignal detection module 39 of FIG. 1, but is carried externally topatient 12. For example, patient 12 may wear biosignal detection module42 on a belt.

Electrode array 44 is positioned on a surface of cranium 16 of patient12 proximate to a motor cortex of brain 16. Electrodes of array 44 arepositioned to detect an EEG signal within a motor cortex of brain 16 ofpatient 12. Electrodes of electrode array 44 are electrically coupled tobiosignal detection module 42 via lead 45.

The position of electrodes of array 44 may depend upon the type ofvolitional patient input that is detected. For example, different musclemovements may produce biosignals within different regions of patient'sbrain 16. In one embodiment, the clinician may initially place array 44based on the general location of the target region (e.g., it is knownthat the motor cortex is a part of the cerebral cortex, which may benear the front of the patient's head) and adjust the location of array44 as necessary to capture the electrical signals from the targetregion. In another embodiment, the clinician may rely on the “10-20”system, which provides guidelines for determining the relationshipbetween a location of an electrode and the underlying area of thecerebral cortex.

In addition, the clinician may locate the particular location within themotor cortex for detecting movement of the specific limb (e.g., afinger, arm or leg) via any suitable technique. In one embodiment, theclinician may also utilize an imaging device, such asmagnetoencephalography (MEG), positron emission tomography (PET) orfunctional magnetic resonance imaging (fMRI) to identify the region ofthe motor cortex of brain 16 associated with movement of the specificlimb. In another embodiment, the clinician may map EEG signals fromdifferent parts of the motor cortex and associate the EEG signals withmovement of the specific limb in order to identify the motor cortexregion associated with the limb. For example, the clinician may attachelectrode array 44 over the region of the motor cortex that exhibitedthe greatest detectable change in EEG signal at the time patient 12actually moved the limb involved in the volitional patient input.

Rather than requiring patient 12 to manually input an indication of atherapy adjustment, e.g., via programmer 30, SCS system 40 automaticallyprovides the indication to IMB 36 upon the detection of a biosignal bybiosignal detection module 42. Biosignal detection module 42 detects EEGsignals of patient 12 and processes the signal to determine whether theEEG signal is indicative of a volitional patient input, i.e., whetherthe biosignal is present. Upon detecting the biosignal, transmits asignal to IMB 36 via wireless telemetry techniques.

In other embodiments, a therapy system described herein may include anIMB 36 positioned to deliver therapy to treat migraine headaches. Forexample, an IMB may include a therapy module that generates and deliverselectrical stimulation to appropriate areas of brain 16 (e.g., theoccipital nerves) to reduce or eliminate migraine headaches. Whenpatient 12 perceives a migraine headache, the patient may generate abiosignal detectable by biosignal detection module 42 or an implantedbiosignal detection module 39 (FIG. 2A) that indicates stimulationtherapy should begin. In this manner, the therapy system may provideon-demand therapy to control a migraine without the need for externalprogrammer 30.

FIG. 3 is a conceptual diagram illustrating another embodiment of atherapy system 46, which includes biosignal detection module 42 coupledto external surface electrode array 44 via lead 45, external cue device54, and programmer 30. Therapy system 46 may be useful for controlling amovement disorder or a neurodegenerative impairment of patient 12, suchas, but not limited to muscle control, motion impairment or othermovement problems, such as rigidity, bradykinesia, rhythmichyperkinesia, nonrhythmic hyperkinesia, akinesia. In some cases, themovement disorder may be a symptom of Parkinson's disease. However, themovement disorder may be attributable to other patient conditions ordiseases

Therapy system 46 may improve the performance of motor tasks by patient12 that may otherwise be difficult. These tasks include at least one ofinitiating movement, maintaining movement, grasping and moving objects,improving gait associated with narrow turns, and so forth. The therapymodule of system 46, i.e., external cue device 54, generates anddelivers a sensory cue, such as a visual, auditory or somatosensory cue,to patient 12 in order to help control some conditions of a movementdisorder. External cues may disrupt certain neural impulses to allowpatient 12 to carry on normal activities. For example, visualstimulation may treat gait freeze associated with Parkinson's disease,nausea, motor impairment, or any other neurological disorder. Forexample, if patient 12 is prone to gait freeze or akinesia, a sensorycue may help patient 12 initiate or maintain movement. In otherembodiments, external cues delivered by external cue device 54 may beuseful for controlling other movement disorder conditions, such as, butnot limited to, rigidity, bradykinesia, rhythmic hyperkinesia, andnonrhythmic hyperkinesia.

Rather than requiring patient 12 to manually activate external cuedevice 54 by interacting with a handheld device or another externaldevice, therapy system 46 automatically activates external cue device 54upon the detection of a biosignal by biosignal detection module 42. Insome cases, therapy system 42 also automatically deactivates externalcue device 54 based on a biosignal. As described with reference to FIG.2A, biosignal detection module 42 detects a biosignal that is generatedwithin brain 16 after patient 16 provides the volitional input, e.g.,upon the generation of a particular volitional thought by patient 12.The volitional input may include, for example, thought of initiating aparticular movement by patient 12. In one embodiment, patient 12 mayopen and close his eyes in a particular pattern that includes a definedinterval between each eye opening and closing. The volitional patientinput may be customized to patient 12. For example, if patient 12 has amovement disorder, the patient input may be selected such that patient12 may provide the input despite an impairment in movement. If patient12 has difficult lifting his arm, for example, the volitional patientinput that provides the biosignal for adjusting therapy should avoidpatient inputs that require patient 12 to lift his arm.

The biosignal is associated with a therapy adjustment, such asinitiating the delivery of an external cue by external cue device 54.Thus, upon detecting the biosignal, biosignal detection module 42transmits a signal to receiver 55 of external cue device 54, and acontroller within external cue device 54 controls the generation anddelivery of a sensory cue to patient 12 in order to help control themovement disorder. Accordingly, biosignal detection module 42 includes atelemetry module that is configured to communicate with receiver 55.Examples of local wireless communication techniques that may be employedto facilitate communication between biosignal detection module 42 andreceiver 55 of device 54 include RF communication according to the802.11 or Bluetooth specification sets, infrared communication, e.g.,according to the IrDA standard, or other standard or proprietarytelemetry protocols. Automatic activation of external cue device 54 uponthe detection of the biosignal may help provide patient 12 with bettercontrol and timing of external cue device 54 by eliminating the need forpatient 12, who exhibits some difficulty with movement, to initiate thedevice 54.

In the embodiment shown in FIG. 3, external cue device 54 is shown as apair of glasses configured to deliver visual stimulation therapy topatient 12 when necessary. For example, external cue device 54 mayinclude one or more light-emitting diode (LED) positioned at specificlocations around the frame of therapy module 54 but within theperipheral vision of patient 12. Alternatively, external cue device 54may include a display configured to produce a light, image, or othervisual aid over the portion of external cue device 54 that is visible topatient 12. Similar to a head-up-display, patient 12 may see the lightpattern in therapy external cue device 54 and the visual therapy fromthe light pattern may help alleviate symptoms of the movement disorder.

As described in further detail with reference to FIG. 6, external cuedevice 54 includes the necessary components to generate and deliver anexternal cue to patient 12. For example, external cue device 54 includesa processor, memory, telemetry circuit to communicate with programmer 30and biosignal detection module 42, light generating circuit, powersource, and any other circuitry necessary for operation. In theembodiment shown in FIG. 3, external cue device 54 is embodied as a pairof glasses, which provides a discreet device for providing therapy topatient 12. In one embodiment, external cue device 16 take the form ofthe Parkinson's goggles developed by the University of Cincinnati, whichincludes a liquid crystal display (LCD) screen that shows a patient atile pattern on the floor to help a patient walk. Other embodiments oftherapy module 54 may include a hat with a brim extending from the browof patient 12, a hand-held device, a display wearable around a necklace,or any other device that may quickly be used by patient 12. These andother embodiments of therapy module 54 are contemplated.

Visual cues, auditory cues or somatosensory cues may have differenteffects on patient 12. For example, in some patients with Parkinson'sdisease, an auditory cue may help the patients grasp moving objects,whereas somatosensory cues may help improve gait and general mobility.Although external cue device 54 is shown as an eyepiece worn by patient12 in the same manner as glasses, in other embodiments, external cuedevice 54 may have different configurations. For example, if an auditorycue is desired, an external cue device may take the form of an ear piece(e.g., an ear piece similar to a hearing aid or head phones). As anotherexample, if a somatosensory cue is desired, an external cue device maytake the form of a device worn on the patient's arm or legs (e.g., as abracelet or anklet), around the patient's waist (e.g., as a belt) orotherwise attached to the patient in a way that permits the patient tosense the somatosensory cue. A device coupled to the patient's wrist,for example, may provide pulsed vibrations.

Programmer 30 allows patient 12 or the clinician to program external cuedevice 54 and/or biosignal detection module 42 at the beginning oftherapy or at anytime during therapy. Programmer 30 may be configured toprogram desired therapy parameters into external cue device 54. Exampletherapy parameters for external cue device 54 may include lightpatterns, light color, light pulse width and pulse rate, and any otherparameters that govern the visual stimulation therapy delivered byexternal cue device 54.

In some embodiments, biosignal detection module 42 and external cuedevice 54 may be incorporated in a common housing. Furthermore, althoughexternal biosignal detection module 42 and external electrode array 44are shown in FIG. 3, in other embodiments, system 46 may include animplanted biosignal detection module 39 and electrode array 25, as shownin FIG. 2A with respect to SCS therapy system 32.

Sensory cues may also be delivered via an IMD. Thus, in otherembodiments of system 46, an IMD may deliver electrical stimulation to asensory location within brain 16 to cause the perception of an externalstimulus. For example, an IMD may deliver stimulation to a visual cortexof brain 16 in order to simulate a visual cue. No external therapymodule may be necessary and the sensory cue would be imperceptible toany other person near patient 12.

FIG. 4 is functional block diagram illustrating components of anexemplary IMD 18 (FIG. 1). In the example of FIG. 4, IMD 18 generatesand delivers electrical stimulation therapy to patient 12. IMD 18includes processor 60, memory 62, stimulation generator 64, biosignaldetection module 66, telemetry circuit 68, and power source 70. Memory62 may include any volatile or non-volatile media, such as a randomaccess memory (RAM), read only memory (ROM), non-volatile RAM (NVRAM),electrically erasable programmable ROM (EEPROM), flash memory, and thelike. Memory 62 may store instructions for execution by processor 60,such as, but not limited to, therapy programs, information identifyingbiosignals (e.g., an amplitude of an EEG signal or a template of an EEGsignal waveform), and any other information regarding therapy of patient12. Therapy information may be recorded for long-term storage andretrieval by a user, and adjustment of the therapy parameters, programs,or biosignal correlations. Memory 62 may include separate memories forstoring instructions, biosignal information, activities, and therapyparameters. In some embodiments, memory 62 stores program instructionsthat, when executed by processor 60, cause IMD 18 and processor 60 toperform the functions attributed to them herein.

Processor 60 controls stimulation generator 64 to deliver electricalstimulation therapy via one or more leads 24. An exemplary range ofelectrical stimulation parameters likely to be effective in deep brainstimulation, for example, are listed below. Other ranges of therapyparameters may be used when the therapy is directed to other tissues.While stimulation pulses are described, stimulation signals may be ofany forms such as sine waves or the like.

1. Frequency: between approximately 0.5 Hz and approximately 500 Hz,such as between approximately 5 Hz and 250 Hz, or between approximately70 Hz and approximately 120 Hz.

2. Amplitude: between approximately 0.1 volts and approximately 50volts, such as between approximately 0.5 volts and approximately 20volts, or approximately 5 volts. In other embodiments, a currentamplitude may be defined as the biological load in the voltage isdelivered.

3. Pulse Width: between approximately 10 microseconds and approximately5000 microseconds, such as between approximately 100 microseconds andapproximately 1000 microseconds, or between approximately 180microseconds and approximately 450 microseconds.

An exemplary range of electrical stimulation parameters likely to beeffective in treating chronic pain, e.g., when applied to spinal cord 34from IMD 36 as in FIGS. 2A and 2B, are listed below. While stimulationpulses are described, stimulation signals may be of any forms such assine waves or the like.

1. Frequency: between approximately 0.5 Hz and approximately 500 Hz,such as between approximately 5 Hz and approximately 250 Hz, or betweenapproximately 10 Hz and approximately 50 Hz.

2. Amplitude: between approximately 0.1 volts and approximately 50volts, such as between approximately 0.5 volts and 20 volts, such asabout 5 volts. In other embodiments, a current amplitude may be definedas the biological load in the voltage is delivered.

3. Pulse Width: between approximately 10 microseconds and approximately5000 microseconds, such as between approximately 100 microseconds andapproximately 1000 microseconds, or between approximately 180microseconds and approximately 450 microseconds.

Processor 60 may include a microprocessor, a controller, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field-programmable gate array (FPGA), discrete logiccircuitry, or the like. Processor 60 controls biosignal detection module66, which receives EEG signals from brain 16 of patient 12 viaelectrodes 26 and lead 28. Processor 60 or a separate processor withinbiosignal detection module 66 analyzes the EEG signals to determinewhether the EEG signals include the biosignal indicative of a volitionalpatient input. That is, processor 60 or a processor within biosignaldetection module 66 determines when the EEG signal indicates thatpatient 12 provided the volitional input because the volitional inputproduces a detectable change in the EEG signal, i.e., detects thebiosignal. While the processing of the EEG signals from biosignaldetection module 66 are primarily described with reference to processor60, in other embodiments, biosignal detection module 66 mayindependently identify a biosignal from patient 12 and notify processor60 when such biosignal has been produced.

If processor 60 detects the biosignal, processor 60 may generate atherapy adjustment indication. The therapy adjustment indication may bea value, flag, or signal that is stored or transmitted to indicatepatient 12 provided a volitional thought indicative of a desiredadjustment to therapy. Processor 60 may transmit the therapy adjustmentindication to a medical device via telemetry module 68, which, inresponse, may adjust therapy accordingly. In this way, the biosignalfrom an EEG signal may be a control signal for adjusting therapy. Insome embodiments, processor 60 may record the therapy adjustmentindication in memory 62 for later retrieval and analysis by a clinician.For example, movement indications may be recorded over time, e.g., in aloop recorder, and may be accompanied by the relevant EEG signal.

Processor 60 may compare the EEG signals from biosignal detection module66 with previously determined biosignal threshold or templates stored inmemory 62 in order to determine whether the EEG signal includes thebiosignal. In this manner, processor 60 determines when to adjusttherapy from the biosignals. Embodiments of signal processing techniquesare described below with reference to FIGS. 10A and 10B.

As various examples of signal processing techniques that processor 60may employ to determine whether the EEG signal includes the biosignal,the EEG signals may be analyzed for voltage, amplitude, temporalcorrelation or frequency correlation with a template signal, orcombinations thereof. For example, the instantaneous or averageamplitude of the EEG signal from within the occipital cortex over aperiod of time may be compared to an amplitude threshold. In oneembodiment, when the amplitude of the EEG signal from within theoccipital cortex is greater than or equal to the threshold value,processor 60 may control stimulation generator 64 to deliver stimulationto patient 12.

As another example, a slope of the amplitude of the EEG signal over timeor timing between inflection points or other critical points in thepattern of the amplitude of the EEG signal over time may be compared totrend information. A correlation between the inflection points in theamplitude waveform of the EEG signal or other critical points and atemplate may indicate the EEG signal includes the biosignal indicativeof patient input. Processor 60 may implement an algorithm thatrecognizes a trend of the EEG signals that characterize the biosignal.If the trend of the EEG signals matches or substantially matches thetrend template, processor 60 may control stimulation generator 64 todeliver stimulation to patient 12.

As another example, processor 60 may perform temporal correlation bysampling the waveform generated by the EEG signal with a sliding windowand comparing the waveform with a stored template waveform that isindicative of the biosignal. For example, processor 60 may perform acorrelation analysis by moving a window along a digitized plot of theamplitude waveform of EEG signals at regular intervals, such as betweenabout one millisecond to about ten millisecond intervals, to define asample of the EEG signal. The sample window is slid along the plot untila correlation is detected between the waveform of the template and thewaveform of the sample of the EEG signal defined by the window. Bymoving the window at regular time intervals, multiple sample periods aredefined. The correlation may be detected by, for example, matchingmultiple points between the template waveform and the waveform of theplot of the EEG signal over time, or by applying any suitablemathematical correlation algorithm between the sample in the samplingwindow and a corresponding set of samples stored in the templatewaveform.

Different frequency bands are associated with different activity inbrain 16. One embodiment of the frequency bands is shown in Table 1:

TABLE 1 Frequency bands Frequency (f) Band Hertz (Hz) FrequencyInformation f < 5 Hz δ (delta frequency band)  5 Hz ≤ f ≤ 10 Hz α (alphafrequency band) 10 Hz ≤ f ≤ 30 Hz β (beta frequency band)  50 Hz ≤ f ≤100 Hz γ (gamma frequency band) 100 Hz ≤ f ≤ 200 Hz high γ (high gammafrequency band)

It is believed that some frequency band components of the EEG signal maybe more revealing of particular activities than other frequencycomponents. For example, the alpha band from Table 1 may be morerevealing of a rest state, in which patient 12 is awake, but not active,than the beta band. EEG signal activity within the alpha band mayattenuate with eye opening or an increase or decrease in physicalactivity. A higher frequency band, such as the beta or gamma bands, mayalso attenuate with an increase or decrease in physical activity.Accordingly, the type of volitional patient input may affect thefrequency band of the EEG signal in which a biosignal associated withthe patient input is detected. The relative power levels within the highgamma band (e.g., about 100 Hz to about 200 Hz) of an EEG signal, aswell as other bioelectric signals, has been shown to be both anexcellent biomarker for motion intent, as well as flexible to humancontrol. That is, a human patient 12 may control activity within thehigh gamma band with volitional thoughts.

The power level within the selected frequency band may be more revealingof the biosignal than a time domain plot of the EEG signal. Thus, insome embodiments, an analog tune amplifier may tune a monitored EEGsignal to a particular frequency band in order to detect the power level(i.e., the signal strength) within a particular frequency band, such asa low frequency band (e.g., the alpha or delta frequency band from Table1), the power level with a high frequency band (e.g., the beta or gammafrequency bands in Table 1) or both the power within the low and highfrequency bands. The biosignal indicative of the volitional patientinput may be the strength of the EEG signal within the tuned frequencyband, a pattern in the strength of the EEG signal over time, a ratio ofpower levels within two or more frequency bands, the pattern in thepower level within two or more frequency bands (e.g., an increase inpower level within the alpha band correlated with a decrease in a powerlevel within the gamma band or high gamma band) or other characteristicsof one or more frequency components of the EEG signal. The power levelof the EEG signal within the tuned frequency band, the pattern of thepower level over time, or the ratio of power levels may be compared to astored value in order to determine whether the biosignal is detected.

The amplifier may be included within processor 60 of IMD 18, a processorof biosignal detection module 66 or another processor used to detect abiosignal from a monitored EEG signal. FIG. 15 illustrates an embodimentof an amplifier circuit that may be used to detect the biosignal, whichmay be included within biosignal detection module 66 or processor 60.The amplifier circuit shown in FIG. 15 uses limited power to monitor afrequency in which a desired biosignal is generated. If the amplifier isdisposed within biosignal detection module 66, processor 60 may controlbiosignal detection module 66 to tune into the desired frequency band,which may be identified during a learning mode or simply by clinicianexperience and specific biosignal research information.

In general, the EEG signal may be analyzed in the frequency domain tocompare the power level of the EEG signal within one or more frequencybands to a threshold or to compare selected frequency components of anamplitude waveform of the EEG signal to corresponding frequencycomponents of a template signal. The template signal may indicate, forexample, a trend in the power level within one or more frequency bandsthat indicates patient 12 generated a volitional input that resulted inthe biosignal indicative of patient input to adjust therapy. Specificexamples of techniques for analyzing the frequency components of the EEGsignal are described below with reference to FIG. 10B.

Telemetry module 68 in IMD 18, as well as telemetry modules in otherdevices described herein, such as programmer 30, may accomplishcommunication by RF communication techniques. In addition, telemetrymodule 68 may communicate with programmer 30 via proximal inductiveinteraction of IMD 18 with external programmer 30. Accordingly,telemetry module 68 may send information to external programmer 30 on acontinuous basis, at periodic intervals, or upon request from theimplantable stimulator or programmer. Processor 60 controls telemetrymodule 68 to send and receive information. Wireless telemetry may beaccomplished by RF communication or proximal inductive interaction ofIMD 18 with external programmer 30.

Power source 70 delivers operating power to various components of IMD18. Power source 70 may include a small rechargeable or non-rechargeablebattery and a power generation circuit to produce the operating power.Recharging may be accomplished through proximal inductive interactionbetween an external charger and an inductive charging coil within IMD18. In some embodiments, power requirements may be small enough to allowIMD 18 to utilize patient motion and implement a kineticenergy-scavenging device to trickle charge a rechargeable battery. Inother embodiments, traditional batteries may be used for a limitedperiod of time. As a further alternative, an external inductive powersupply could transcutaneously power IMD 18 whenever measurements areneeded or desired.

IMD 36 (FIG. 2A) is substantially similar to IMD 18 shown in FIG. 4, butdoes not include biosignal detection module 66. The telemetry module ofIMD 36 is configured to communicate with the separately housed biosignaldetection module 39 via wireless telemetry techniques, such as RFcommunication.

FIG. 5 is functional block diagram illustrating components of anexemplary medical device 72 with drug pump 78. Medical device 72 may beused in therapy system 10 (FIG. 1) or other therapy systems in whichvolitional patient input generates a biosignal within the patient'sbrain that is used as feedback to adjust therapy delivered by medicaldevice 72. Medical device 72 may be implanted or carried externally topatient 12. As shown in FIG. 5, medical device 72 includes processor 74,memory 76, drug pump 78, biosignal detection module 80, telemetry module84, and power source 86. Drug pump 78 delivers a specific quantity of apharmaceutical agent to a desired tissue within patient 12 via catheter79 implanted within patient 12. In some embodiments, medical device 72may include stimulation generator for producing electrical stimulationin addition to delivering drug therapy.

Medical device 72 may be directed towards chronic pain therapy, butmedical device 72 may deliver a drug (i.e., a pharmaceutical agent) oranother fluid to any location within patient 12. Processor 74, memory76, biosignal detection module 80, telemetry module 84, and power source86 may all be similar to processor 60, memory 62, biosignal detectionmodule 66, telemetry module 68, and power source 70, respectively, ofFIG. 4. Processor 74 controls the operation of medical device 72 withthe aid of instructions that are stored in memory 76, which is similarto the control of IMD 18. For example, the instructions may dictate thebolus size of a drug that is delivered to patient 12 when biosignaldetection module 80 detects the biosignal indicative of volitionalpatient input relating to a therapy adjustment action. When processor 74receives an indication from biosignal detection module 80 that patient12 has provided a volitional input that is associated with a drugdelivery adjustment action (e.g., initiation of drug delivery, increaseor decrease in bolus size or frequency or deactivation of drugdelivery), processor 74 controls drug pump 78 to take the actionassociated with the biosignal. As mentioned above, the biosignal may beindicative of some kind of volitional patient activity, such as eyemovement, blinking, facial movements, or other volitional thoughts.

Biosignal detection module 80 is substantially similar to biosignaldetection module 66 of FIG. 4. Biosignal detection module 80 may includean analog circuit that amplifies and monitors a specific frequency bandof the electrical signal from brain 16. Memory 76 may store thebiosignal information that determines which frequency bands of the EEGsignal to monitor and what thresholds in signal amplitude indicate asuccessful biosignal. Biosignal detection module 80 may also beconnected to an electrode array, such as implanted array 25 (FIG. 1) orexternal array 44 (FIG. 2B), via lead 82 or via wireless telemetry.

In alternative embodiments of IMD 18 and medical device 72, therespective biosignal detection modules 66, 80 may be disposed in aseparate housing. For example, in FIG. 2A, therapy system 32 includes aseparate IMD 36 and biosignal detection module 39. In such embodiments,biosignal detection modules 66, 80 may communicate wirelessly with themedical device, thereby eliminating the lead or other elongated memberthat couples the biosignal detection module to IMD 18 or medical device72. In some embodiments, biosignal detection module 66 may include anamplifier circuit (e.g., the circuit shown in FIG. 15) for monitoringand identifying biosignals within brain 16 with a relatively minimalamount of battery power consumption.

FIG. 6 is a functional block diagram illustrating components of anembodiment of therapy module 88, which may be incorporated into anexternal cue device, such as device 54 of FIG. 3. In addition, therapymodule 88 may have similar components to IMD 18. For example, processor90, memory 92, telemetry module 98, and power source 100 may be similarto processor 60, memory 62, telemetry module 68, and power source 70 ofIMD 18.

As shown in FIG. 6, therapy module 88 includes cue generator 94 coupledto output device 96. Upon receiving a control signal from biosignaldetection module 42 that indicates biosignal detection module 42detected the biosignal indicative of a volitional patient input,processor 90 controls cue generator 94 to generate a sensory cue anddeliver the cue to patient via output device 96. As previouslydescribed, biosignal detection module 42 detects and identifiesbiosignals produced by patient 12 when the patient provides anindication that a therapy adjustment is desired. For example, patient 12may create a volitional thought to generate a biosignal when the patientneeds a visual cue from output device 96. Processor 90 acts upon theidentification of the biosignal and controls cue generator 94 togenerate a sensory cue in accordance with the type of biosignalidentified. In this manner, patient 12 may generate multiple types ofbiosignals through volitional thought in order to elicit multiple typesof sensory cues from therapy module 88.

Output device 96 may be any device configured to create a stimulus. Aspreviously described, example stimuli may include light, sound,vibration, any combination thereof or other visual, auditory orsomatosensory cues. As described in FIG. 3, output device 96 may be anLED mounted on the inside of the frame of therapy device 18 or an LCDscreen. In some embodiments, therapy module 88 may include multipleoutput devices 96 that each deliver a different stimuli.

As described above, wireless telemetry in therapy module 88 may beneeded to communicate with biosignal detection module 42, programmer 30,or another device. Wireless communication may be accomplished by RFcommunication or proximal inductive interaction of therapy module 88with the other wireless device. Accordingly, telemetry module 98 maysend or receive information from biosignal detection module 42 andexternal programmer 56 on a continuous basis, at periodic intervals, orupon request from the implantable stimulator or programmer. Processor 90controls telemetry module 98 to send and receive information.

Cue generator 94 includes the electrical circuitry needed to generatethe stimulus delivered by output device 96. For example, cue generator94 may modulate the color of light emitted by output device 96, theintensity of light emitted by output device 96, the frequency of soundwaved delivered by output device 96, or any other therapy parameter ofthe output device. Processor 90 may interrogate therapy parameterinstructions stored in memory 92 before controlling any specificstimulus generated by cue generator 94.

In some embodiments, output device 96 may be a display that is capableof producing patterns of light, images, or other representations on theoutput device itself or projected onto another surface for patient 12 tosee. In this manner, the visual cue, or stimulus, may be more complexthan a simple light or sound. For example, output device 96 may delivera sequence of colored shapes that causes the symptoms of the patient 12condition to subside. Alternatively, one or more words, numbers, symbolsor other graphics may produce a desired affect to treat patient 12. Whenoutput device 96 is a display, the output device may be embodied as aLCD, head-up display, LCD projection, or any other display technologyavailable to the manufacturer of therapy module 88.

FIG. 7 is a functional block diagram illustrating components ofbiosignal detection module 200 that is separate from a therapy module.For example, biosignal detection module 200 may be an implantedbiosignal detection module 39 of FIG. 2A or an external biosignaldetection module 42 of therapy system 32 of FIGS. 2A and 3. Biosignaldetection module 200 provides feedback to control a medical device, suchas IMD 36 or external cue device 54. Biosignal detection module 200includes EEG sensing module 202, processor 204, telemetry module 206,memory 208, and power source 210. Biosignal detection modules 66, 80 ofIMD 18 and medical device 72, respectively, may also include somecomponents of biosignal detection module 200 shown in FIG. 7, such asEEG sensing module 202 and processor 204.

EEG sensing module 202, processor 204, as well as other components ofbiosignal detection module 200 that require power may be coupled topower source 210. Power source 210 may take the form of a rechargeableor non-rechargeable battery. EEG sensing module 202 monitors an EEGsignal within brain 16 of patient 12 via electrodes 212A-E, which maybe, for example, a part of electrode array 25 (FIG. 2A) or electrodearray 44 (FIG. 3). Electrodes 212A-E are coupled to EEG sensing module202 via leads 214A-E, respectively. Two or more of leads 214A-E may bebundled together (e.g., as separate conductors within a common leadbody) or may include separate lead bodies.

Processor 204 may include a microprocessor, a controller, a DSP, anASIC, a FPGA, discrete logic circuitry or the like. Processor 204controls telemetry module 206 to exchange information with programmer 30and/or a medical device, such as IMD 36. Telemetry module 206 mayinclude the circuitry necessary for communicating with programmer 30 oran implanted or external medical device. Examples of wirelesscommunication techniques that telemetry module 206 may employ include RFcommunication, infrared communication, e.g., according to the IrDAstandard, or other standard or proprietary telemetry protocols.

In some embodiments, biosignal detection module 200 may include separatetelemetry modules for communicating with programmer 30 and the medicaldevice. Telemetry module 206 may operate as a transceiver that receivestelemetry signals from programmer 30 or a medical device, and transmitstelemetry signals to the programmer 30 or medical device. For example,processor 204 may control the transmission of the EEG signals from EEGsensing module 202 to a medical device. As another example, processor204 may determine whether the EEG signal monitored by EEG sensing module202 includes the biosignal, and upon detecting the presence of thebiosignal, processor 204 may transmit a control signal to the medicaldevice via telemetry module 206, where the control signal indicates thetype of therapy adjustment indicated by the biosignal.

In some embodiments, processor 204 stores monitored EEG signals inmemory 208. Memory 208 may include any volatile or non-volatile media,such as a RAM, ROM, NVRAM, EEPROM, flash memory, and the like. Memory208 may also store program instructions that, when executed by processor204, cause EEG sensing module 202 to monitor the EEG signal of brain 16.Accordingly, computer-readable media storing instructions may beprovided to cause processor 204 to provide functionality as describedherein.

EEG sensing module 202 includes circuitry that measures the electricalactivity of a particular region, e.g., motor cortex, within brain 16 viaelectrodes 212A-E. EEG sensing module 202 may acquire the EEG signalsubstantially continuously or at regular intervals, such as at afrequency of about 1 Hz to about 100 Hz. EEG sensing module 202 includescircuitry for determining a voltage difference between two electrodes212A-E, which generally indicates the electrical activity within theparticular region of brain 16. One of the electrodes 212A-E may act as areference electrode. An example circuit that EEG sensing module 40 mayinclude is shown and described below with reference to FIGS. 15-20. TheEEG signals measured from via external electrodes 212A-E may generate avoltage in a range of about 5 microvolts (μV) to about 100 μV.

The output of EEG sensing module 202 may be received by processor 204.Processor 204 may apply additional processing to the EEG signals, e.g.,convert the output to digital values for processing and/or amplify theEEG signal. In some cases, a gain of about 90 decibels (dB) is desirableto amplify the EEG signals. In some embodiments, EEG sensing module 202or processor 204 may filter the signal from electrodes 212A-E in orderto remove undesirable artifacts from the signal, such as noise fromelectrocardiogram signals, electromyogram signals, and electro-oculogramsignals generated within the body of patient 12.

Processor 204 may determine whether the EEG signal from EEG sensingmodule 202 includes the biosignal indicative of a volitional patientinput via any suitable technique, such as the techniques described abovewith respect to processor 60 (FIG. 4) of IMD 18. If processor 204detects the biosignal from the EEG signal, processor 204 may generate atherapy adjustment indication. The therapy adjustment indication may bea value, flag, or signal that is stored or transmitted to indicatepatient 12 provided a volitional thought indicative of a desiredadjustment to therapy. Processor 204 may transmit the therapy adjustmentindication to a medical device via telemetry module 206, and the medicaldevice may adjust therapy according to the therapy adjustment actionassociated with the biosignal or therapy adjustment indication. In thisway, the biosignal from an EEG signal may be a control signal foradjusting therapy. In some embodiments, processor 204 may record thetherapy adjustment indication in memory 208 for later retrieval andanalysis by a clinician. For example, movement indications may berecorded over time, e.g., in a loop recorder, and may be accompanied bythe relevant EEG signal.

In other embodiments, rather than generating a therapy adjustmentindication, processor 204 may merely control the transmission of the EEGsignal from EEG sensing module 202 to a medical device. The medicaldevice may then determine whether the EEG signal includes the biosignal.

FIG. 8 is functional block diagram illustrating components of anexemplary external programmer 30. External programmer 30 includesprocessor 101, memory 102, user interface 103, telemetry module 104, andpower source 105. Processor 101 controls user interface 103 andtelemetry module 104, and stores and retrieves information andinstructions to and from memory 102. Programmer 30 may be configured foruse as a clinician programmer or a patient programmer.

Programmer 30 may be used to select therapy programs (e.g., sets ofstimulation parameters), generate new therapy programs, modify therapyprograms through individual or global adjustments, transmit the newprograms to a medical device, such as IMD 18 or IMD 36, and correlatebiosignals with specific patient 12 activities and/or therapyadjustments. In a learning mode, programmer 30 may allow patient 12and/or the clinician to create a volitional patient input and instructIMD 18 to identify the resulting biosignal in brain 16.

Programmer 30 may also be used to correlate biosignals with desiredtherapy adjustments. Once the correlation between biosignals andvolitional patient thoughts, as well as particular biosignals andparticular therapy adjustments is completed, the correlated biosignalsmay be uploaded to a biosignal detection module for incorporation into aclosed loop therapy control system. The resulting detection of thebiosignal causes a therapy adjustment. Example therapy adjustments thatmay be correlated to biosignals include turning therapy on and off,increasing therapy amplitude, decreasing therapy amplitude, and changingtherapy programs. While programmer 30 may be most useful when initiallyprogramming IMD 18, programmer 30 may be continually used throughouttherapy to correct any problems with therapy.

The user, either a clinician or patient 12, may interact with programmer30 through user interface 103. User interface 103 includes a display(not shown), such as an LCD or other screen, to show information relatedto stimulation therapy and input controls (not shown) to provide inputto programmer 30. Input controls may include the buttons described inFIG. 12. Processor 101 monitors activity from the input controls andcontrols the display or stimulation function accordingly. In someembodiments, the display may be a touch screen that enables the user toselect options directly from the display. In other embodiments, userinterface 103 also includes audio circuitry for providing audibleinstructions or sounds to patient 12 and/or receiving voice commandsfrom patient 12.

Memory 102 may include instructions for operating user interface 103,telemetry module 104 and managing power source 105. Memory 102 alsoincludes instructions for managing biosignals and correlated therapyadjustments executable by processor 101. In addition, memory 102 mayinclude instructions for guiding patient 12 through the learning modewhen correlating biosignals to therapy adjustments and/or activities.Memory 102 may also store any therapy data retrieved from therapy device18 during the course of therapy. The clinician may use this therapy datato determine the progression of patient 12 disease in order to predictfuture treatment.

Memory 102 may include any volatile or nonvolatile memory, such as RAM,ROM, EEPROM or flash memory. Memory 102 may also include a removablememory portion that may be used to provide memory updates or increasesin memory capacities. A removable memory may also allow sensitivepatient data to be removed before programmer 30 is used by a differentpatient. Processor 101 may comprise any combination of one or moreprocessors including one or more microprocessors, DSPs, ASICs, FPGAs, orother equivalent integrated or discrete logic circuitry. Accordingly,processor 101 may include any suitable structure, whether in hardware,software, firmware, or any combination thereof, to perform the functionsascribed herein to processor 101.

Wireless telemetry in programmer 30 may be accomplished by RFcommunication or proximal inductive interaction of external programmer30 with therapy device 18. This wireless communication is possiblethrough the use of telemetry module 104. Accordingly, telemetry module104 may be similar to the telemetry module contained within therapydevice 18. In alternative embodiments, programmer 30 may be capable ofinfrared communication or direct communication through a wiredconnection. In this manner, other external devices may be capable ofcommunicating with programmer 30 without needing to establish a securewireless connection.

Power source 105 delivers operating power to the components ofprogrammer 30. Power source 105 may include a battery and a powergeneration circuit to produce the operating power. In some embodiments,the battery may be rechargeable to allow extended operation. Rechargingmay be accomplished electrically coupling power source 105 to a cradleor plug that is connected to an alternating current (AC) outlet. Inaddition, recharging may be accomplished through proximal inductiveinteraction between an external charger and an inductive charging coilwithin programmer 30. In other embodiments, traditional batteries (e.g.,nickel cadmium or lithium ion batteries) may be used. In addition,programmer 30 may be directly coupled to an alternating current outletto operate. Power source 105 may include circuitry to monitor powerremaining within a battery. In this manner, user interface 103 mayprovide a current battery level indicator or low battery level indicatorwhen the battery needs to be replaced or recharged. In some cases, powersource 105 may be capable of estimating the remaining time of operationusing the current battery.

FIG. 9A illustrates a flow diagram of a technique for controlling atherapy device, such as IMD 18 (FIG. 1), IMD 36 (FIG. 2A) or externalcue device 54 (FIG. 3) based on a biosignal within brain 16 that resultsfrom a volitional patient input. While FIGS. 9A and 10A-B and 14 areprimarily described with reference to biosignal detection module 200(FIG. 7) and IMD 36 (FIG. 2), in other embodiments, the technique shownin FIG. 9A may be employed by any therapy system that includes abiosignal detection module and a therapy delivery device, such as IMD18, which includes both a biosignal detection module 66 and astimulation generator 64.

EEG sensing module 202 (FIG. 7) of biosignal detection module 200monitors the EEG signal within the motor cortex of brain 16 viaelectrodes 212A-E continuously or at regular intervals (220). In otherembodiments, EEG sensing module 202 may monitor the EEG signal withinanother part of brain 16, such as the sensory motor strip or occipitalcortex. Processor 204 (FIG. 7) of biosignal detection module 200receives the EEG signals from EEG sensing module 202 and processes theEEG signals to determine whether the EEG signals indicate patient 12 hasgenerated the volitional patient input indicative of a desired therapyadjustment action, i.e., whether the biosignal is detected (222). Asignal processor within processor 202 may determine whether the EEGsignals include the biosignal using any suitable technique, such as thetechniques described above (e.g., voltage, amplitude, temporalcorrelation or frequency correlation with a template signal, orcombinations thereof).

If the biosignal is not present in the monitored EEG signals, EEGsensing module 202 may continue monitoring the EEG signal under thecontrol of processor 204 (220). If the biosignal is detected, processor204 may implement control of a therapy device (224). For example, in thecase of external cue device 54 (FIG. 3), processor 204 may generate atherapy adjustment indication and transmit the indication to processor90 (FIG. 6) of external cue device 54 via telemetry module 206, andprocessor 90 may cause cue generator 94 to deliver a visual cue topatient 12. As another example, in the case of IMD 36 of FIG. 2A, upondetecting the presence of the biosignal in the EEG signals, processor204 of biosignal detection module 200 may provide a signal to aprocessor of IMD 36 via the respective telemetry modules. The processorof IMD 36 may then initiate therapy delivery via the stimulationgenerator or adjust therapy (e.g., increase the amplitude of stimulationin order to help patient 12 initiate muscle movement). After controllinga therapy device, the processor 204 may continue monitoring the EEGsignal for a biosignal.

FIG. 9B is a flow diagram illustrating another embodiment of a techniquefor initiating therapy delivery based on a biosignal indicative of avolitional patient input relating to a desired therapy adjustmentaction. While FIG. 9B is described primarily with reference to IMD 18,which includes biosignal detection module 66, in other embodiments,other devices or combination of devices, such as IMD 36 and biosignaldetection module 42, may implement the technique shown in FIG. 9B. Asshown in FIG. 9B, IMD 18 may be in standby mode as patient 12, duringwhich patient 12 is not currently receiving therapy or is receiving aminimal amount of therapy (106). Biosignal detection module 66 monitorsan EEG signal to determine whether the EEG signal includes a biosignalthat indicates patient 12 provided a volitional input, such as a thoughtrelating to a particular muscle movement, to initiate therapy (107). Ifbiosignal detection module 66 does not detect the biosignal, IMD 18remains in standby mode. If biosignal detection module 66 detects thebiosignal within the monitored EEG processor 60 may control stimulationgenerator 64 (FIG. 4) to deliver therapy to patient 12 (108).

Stimulation generator 64 may continue delivering therapy to patient 12for a predetermined amount of time or until processor 60 detects asignal that indicates therapy should be adjusted (e.g., stopped). Thesignal may take the form of a patient input (e.g., via programmer 30, animplanted accelerometer or via a biosignal generated in response to avolitional patient though). Using the latter signal as an example, ifbiosignal detection module 66 does not detect a biosignal that indicatespatient 12 provided an input to stop therapy (109), therapy continues(108). However, if detection module 66 detects another “adjust therapy”biosignal (109), processor 60 controls stimulation generator 64 to takethe associated therapy adjustment (110). For example, if the biosignalis indicative of a patient input to stop therapy delivery, processor 60controls stimulation generator 64 to stop delivery of electricalstimulation to patient 12. For example, if IMD 18 determines that thebiosignal directs the therapy module to stop therapy (110), IMD 18 stopstherapy, and may return to a standby mode.

FIG. 10A is a flow diagram of an embodiment of a technique fordetermining whether an EEG signal includes a biosignal indicative of avolitional patient thought relating to a desired therapy adjustmentaction. EEG sensing module 202 (FIG. 7) of biosignal detection module200 monitors the EEG signal within the motor cortex of brain 16 viaelectrodes 212A-E continuously or at regular intervals (220), such as ata measurement frequency of about one hertz (Hz) to about 100 Hz. Inother embodiments, EEG sensing module 202 may monitor the EEG signalwithin another part of brain 16, such as the sensory motor strip oroccipital cortex. Processor 204 of biosignal detection module 200compares the amplitude of the EEG signal waveform to a stored thresholdvalue (226). The relevant amplitude may be, for example, theinstantaneous amplitude of an incoming EEG signal or an averageamplitude of the EEG signal over period of time. In one embodiment, thethreshold value is determined during the trial phase that precedesimplantation of a chronic therapy delivery device within patient 12.

In one embodiment, if the monitored EEG signal waveform comprises anamplitude that is less than the threshold value (228), processor 204does not generate any control signal to adjust therapy delivery. On theother hand, if the monitored EEG signal waveform comprises an amplitudethat is greater than or equal to the threshold value (228), the EEGsignal includes the biosignal indicative of the volitional patientinput, and processor 204 may implement control of a therapy device(224). In other embodiments, depending on the type of volitional patientinput as well as the region of brain 16 in which the EEG signals aremonitored, processor 204 may implement control of a therapy device ifthe amplitude of the EEG signal falls below a threshold value. A trialphase may be useful for determining the appropriate relationship betweenthe threshold of the EEG signal and the threshold value.

FIG. 10B is a flow diagram of another embodiment of a technique fordetermining whether an EEG signal includes a biosignal indicative of avolitional patient input associated with a desired therapy adjustmentaction. EEG sensing module 202 (FIG. 7) of biosignal detection module200 monitors the EEG signal within the motor cortex of brain 16 viaelectrodes 212A-E continuously or at regular intervals (220), such as ata measurement frequency of about one hertz (Hz) to about 100 Hz. Inother embodiments, EEG sensing module 202 may monitor the EEG signalwithin another part of brain 16, such as the sensory motor strip oroccipital cortex.

A signal processor within processor 204 of biosignal detection module200 extracts one or more frequency band components of the monitored EEGsignal (230) in order to determine whether the biosignal is detected. Inthe embodiment shown in FIG. 10B, processor 204 compares the pattern inthe EEG signal strength (i.e., the power level) within one frequencybands with a template (232). In this way, processor 204 may use signalanalysis techniques, such as correlation, to implement a closed-loopedsystem for adjusting therapy.

If the pattern of the EEG signal correlates well, i.e., matches, with apattern template (232), processor 204 of biosignal detection module 200controls a medical device (e.g., initiates therapy, deactivates therapyor increases or decreases a therapy parameter) (224). In someembodiments, the template matching algorithm that is employed todetermine whether the pattern in the EEG signal matches the template maynot require a one hundred percent (100%) correlation match, but rathermay only match some percentage of the pattern. For example, if themonitored EEG signal exhibit a pattern that matches about 75% or more ofthe template, the algorithm may determine that there is a substantialmatch between the pattern and the template, and the biosignal isdetected. In other embodiments, processor 204 may compare a pattern inthe amplitude waveform of the EEG signal (i.e., in the time domain) witha template. The pattern template for either the template matchingtechniques employed in either the frequency domain or the time domainmay be generated in a trial phase, an example of which is shown in FIG.14 and described below.

FIG. 11 is an example EEG signal within an occipital cortex of brain 16of patient 12, where the EEG signal is received by biosignal detectionmodule 200 and is indicative of when patient 12 closes and opens theeyelids. Biosignal detection module 200 may be incorporated into any ofIMDs 16, 36, biosignal detection module 42, external cue device 54 orother devices that are capable of detecting the EEG signal shown in FIG.11 when electrodes are positioned over the occipital cortex of brain 16.As shown in FIG. 11, the EEG signal has been tuned to the alphafrequency band, and in particular, approximately 10 Hz. In FIG. 11, the10 Hz frequency band component of the EEG signal is plotted asvoltage/power (uV²) versus time (seconds). The resulting amplitudechanges in the EEG signal are identifiable between moments when the eyesof patient 12 are closed and open. Thus, FIG. 11 illustrates an exampleof a pattern in the EEG signal strength within the alpha frequency band,where the pattern shown indicates the monitored EEG signal included thebiosignal.

When the eyes of patient 12 are open, the biosignal oscillates between(0.005 uV)² and −(0.005 uV)². However, the signal changes in amplitudewhen the eyes of patient 12 are closed, as indicated by “EC” in FIG. 11.Volitional thought created by patient 12 that resulted in closing theeyes generated a biosignal with amplitudes approaching (0.015 uV)² and−(0.015 uV)². The increase in the amplitude of the alpha band componentof the EEG signal for a certain duration of time, such as two seconds,may be selected as a biosignal for used in a closed loop therapy system.For example, biosignal detection module 42 may monitor the alpha bandcomponent of the EEG signal, tuned to about 10 Hz, and upon detecting apower level that exceeds a threshold window of −(0.01 uV)² to (0.01 uV)²for a duration of two or more seconds, biosignal detection module 42 maygenerate a control signal for adjusting therapy delivery to patient 12.Thus, the biosignal is indicative of a volitional patient input in theform of the patient closing his eyes for a certain period of time.Alternatively, therapy module may identify absolute amplitude valuesgreater than (0.02 uV)².

In order to minimize the possibility that patient 12 may inadvertentlyactivate the therapy adjustment by closing his eyes, biosignal detectionmodule 42 may be configured to identify a particular pattern in thesignal strength (measured in voltage/power) in the 10 Hz frequency band.Therefore, patient 12 may set up a pattern in closing eyes that must bedetected before therapy changes are performed. For example, patient 12may program IMD 18 to detect five separate eyes closed events within a10 second period before therapy is to be delivered. As another example,the pattern in the signal strength shown in FIG. 11 is generated whenpatient 12 closes his eyes for about two seconds, opens his eyes forabout four seconds, closes his eyes for about two seconds, opens hiseyes for about ten seconds, and closes his eyes again for about twoseconds. Biosignal detection module 42 may use this biosignal torecognize a volitional patient input from patient 12. Other patterns arealso contemplated.

Another technique for minimizing the possibility that patient 12 mayinadvertently provide a volitional thought that activates the therapyadjustment may be combining the biosignal detection with another inputmechanism. In one embodiment, for example, patient 12 may tap anexternal or implanted accelerometer, which is coupled to biosignaldetection module 42 via a wired connection or a wireless connection.Biosignal detection module 42 may recognize the tapping (e.g., tappingin a particular pattern) as a confirmation that patient 12 purposefullygenerated the biosignal to adjust therapy.

The 10 Hz component of an EEG signal shown in FIG. 11 is an example ofone biosignal that biosignal detection module 200 may identify in orderto initiate an adjustment to therapy delivery. Biosignal detectionmodule 200 may monitor multiple different biosignals of differentfrequency bands and/or at different locations within brain 16. Patient12 may utilize any of these biosignals in creating a pattern ofvolitional inputs necessary for IMD 18 (or another device) to adjusttherapy. Biosignal detection module 200 may be configured to detect morethan one type of biosignal indicative of a volitional patient thought.For example, one biosignal may increase an amplitude of stimulation,while another biosignal may turn therapy off or into a safe mode.

FIG. 12 illustrates an embodiment of programmer 30, which includes userinterface 116 for receiving input from a user, such as patient 12 or aclinician, and displaying information to the user. Programmer 30 is ahandheld computing device that is useful for learning and matching EEGsignals to volitional patient thoughts in order to define biosignals forimplementation into a closed loop therapy system. Programmer 30 includesouter housing 113, which encloses circuitry necessary for programmer 30to operate. Housing 113 may be constructed of a polymer, metal alloy,composite, or combination material suitable to protect and containcomponents of programmer 30. In addition, housing 113 may be partiallyor completely sealed such that fluids, gases, or other elements may notpenetrate the housing and affect components therein.

Programmer 30 also includes display 114, select button 118, control pad120 with directional buttons 122, 124, 126 and 128, increase button 132,decrease button 130, contrast buttons 134 and 136, and power button 138.Power button 138 turns programmer 30 on or off. Programmer 30 mayinclude safety features to prevent programmer 30 from shutting downduring a telemetry session with IMD 18 or another device in order toprevent the loss of transmitted data or the stalling of normaloperation. Alternatively, programmer 30 and IMD 18 may includeinstructions which handle possible unplanned telemetry interruption,such as battery failure or inadvertent device shutdown. While IMD 18 isprimarily referred to throughout the discussion of FIG. 12, in otherembodiments, programmer 30 may be configured to communicate with othermedical devices, such as IMD 36 (FIG. 2) or external cue device 54 (FIG.3). Furthermore, while patient 12 is primarily referred to throughoutthe discussion of FIG. 12, in other embodiments, other users may useprogrammer 30.

Display 114 may be an LCD or another type of monochrome or color displaycapable of presenting information to patient 12. Contrast buttons 134and 136 may be used to control the contrast of display 114. Display 114may provide information regarding the current mode, selections forpatient 12, and operational status of programmer 30. Control pad 120allows patient 12 to navigate through items presented on display 114.Patient 12 may press control pad 120 on any of arrows 122, 124, 126 and128 in order to move between items presented on display 114 or move toanother screen not currently shown by display 114. For example, patient12 may depress or otherwise activate arrows 122 and 126 to navigatebetween screens of user interface 116. Patient 12 may press selectbutton 118 to select any highlighted element in user interface 116. Insome embodiments, the middle portion of control pad 120 may provide a“select” button that enables patient 12 to select a particular itempresented on display 114, such as an item that is highlighted on display114. In other embodiments, scroll bars, a touch pad, scroll wheel,individual buttons, or a joystick may perform the complete or partialfunction of control pad 120.

Decrease button 130 and increase button 132 provide input mechanisms forpatient 12. In general, depressing decrease button 130 one or more timesmay decrease the value of a highlighted therapy parameter and depressingincrease button 132 one or more times may increase the value of ahighlighted therapy parameter. While buttons 130 and 132 may be used tocontrol the value of any therapy parameter, patient 12 may also utilizebuttons 130 and 132 to select particular programs during a therapysession. Buttons 130 and 132 may alternatively decrease or increase thethresholds required for identifying biosignals. For example, patient 12may enter learning mode 146 of programmer 30 and decrease thesensitivity of the biosignal detection if therapy adjustments areoccurring at a greater frequency than desired. In other embodiments,control pad 120 may be the only input that patient 12 may use tonavigate through the screens and menus of programmer 30.

Programmer 30 may take other shapes or sizes not described herein. Forexample, programmer 30 may take the form of a clam-shell shape, similarto cellular phone designs. When programmer 30 is closed, some or allelements of the user interface may be protected within the programmer.When programmer 30 is open, one side of the programmer may contain adisplay while the other side may contain input mechanisms. In any shape,programmer 30 may be capable of performing the requirements describedherein.

In alternative embodiments, the buttons of programmer 30 may performdifferent functions than the functions provided in FIG. 12 as anexample. In addition, other embodiments of programmer 30 may includedifferent button layouts or number of buttons. For example, display 114may be a touch screen that incorporates all user interfacefunctionality.

In FIG. 12, learning mode 146 is presented on user interface 116. In thelearning mode 146, programmer 30 correlates an EEG signal with thevolitional input. For example, patient 12 may move his index finger in aparticular pattern, and programmer 30 may correlate the monitored EEGsignal at the time the patient 12 moved his index finger with themovement. A clinician, with the aid of a computing device, may extract abiosignal (e.g., a particular frequency component of the EEG signal)from the correlated EEG signal. The frequency band in which the EEGsignal exhibits a noticeable change or characteristic may be selected atthis stage. Biosignal icon 140 indicates whether biosignal detectionmodule 42 is currently active and monitoring EEG signals, either as apart of learning mode 146 or during implementation of a chronic therapysystem. In the embodiment shown in FIG. 12, biosignal icon 140 indicatesthat biosignal detection module 200 (or another biosignal detectionmodule) is currently active and monitoring EEG signals because icon 140is darkened with lines extending from the head in icon 140. In contrast,when biosignal icon 140 is merely an outline and not filled in,biosignal icon 140 indicates that biosignal detection module 200 is notmonitoring EEG signals.

Stimulation icon 142 indicates whether therapy is being delivered topatient 12. In the embodiment shown in FIG. 12, the lightning bolt ofstimulation icon 142 is not highlighted, thereby indicating that thattherapy is not currently being delivered. In embodiments in which atherapy system delivers a therapy other than electrical stimulation,stimulation icon 142 may have a different configuration.

Activity field 148 of the learning mode 146 user interface 116 ispopulated with possible activities for generating the volitional patientinput. Scroll bar 150 indicates that more activates are available lowerin the field. The activities may include physical activities (e.g.,muscle movement) as well as mental activities (e.g., a focused task,such as performing a mathematical calculation, spelling a word, recitingany combination of letters, words, numbers, symbols, sounds, and soforth). Patient 12 may use control pad 120 to select an activity fromactivity field 148. As shown, “Eyes Open” is highlighted. Patient 12 mayvoluntarily keep his eyes open while pressing select button 118. Inresponse, programmer 30 may provide a signal to biosignal detectionmodule 200 via telemetry module 104, and biosignal detection module 42may monitor the EEG signal that corresponds to the patient's volitionalthought relating to keeping his eyes open. Biosignal detection module200 may record the corresponding EEG signal or may transmit the EEGsignal to programmer 30, which may store the EEG signal in memory 102(FIG. 8).

As previously described, programmer 30 or a clinician, with the aid ofprogrammer 30 or another computing device, may extract a biosignal(e.g., a particular frequency component of the EEG signal, the amplitudeof the EEG signal, a pattern in the amplitude waveform of the EEGsignal, and so forth) from the EEG signal that corresponds to theselected activity from activity field 148. Programmer 30 may store thebiosignal within memory 102 and upload the biosignal to biosignaldetection module 200, IMD 18 or another medical device for future use.Patient 12 may subsequently select “Eyes Closed” from activity field 148when closing his eyes to allow biosignal detection module 42 to extractthe contrasting biosignal from the EEG signal associated with the “eyesclosed” state. If desired, patient 12 may complete each of theactivities in the activity field 148 in this manner until all thedesired activities have been correlated with detected biosignals.

Programmer 30 may deliver a warning message to patient 12 if thecorrelation between an EEG signal and activity was unsuccessful.Programmer 30 may then prompt patient 12 to provide the input relatingto the selected activity or select another activity to correlate with abiosignal. Additionally, programmer 30 may request that patient 12repeat the correlation at least one time before the correlation betweenthe activity and biosignal is stored. In some embodiments, programmer 30may guide patient 12 through the learning mode 146. Programmer 30 mayprompt patient 12 for each activity and automate the process to the mostcommon activities used in controlling therapy adjustments withvolitional cues.

Patient 12 may also navigate to another screen to review the biosignalsthat have been identified. Programmer 30 may also allow patient 12 toreturn to learning mode 146 to repeat certain activities or regeneratecertain biosignals if desired. In some cases, patient 12 may be able toenter new activities not populated in activity field 148. For example,patient 12 may desire to use a volitional cue not normally desired byother patients. The clinician may enable or disable any of these customapplications of programmer 30, depending upon the ability of patient 12to utilize the features without hindering effective therapy.

After determining one or more biosignals indicative of a volitionalpatient thought, programmer 30 or the clinician with the aid ofprogrammer 30 or another computing device, may associate the one or morebiosignals to one or more therapy adjustments. For example, using the“eyes open” and “eyes closed” biosignals, the clinician may associate aparticular pattern of the patient's “eyes open” biosignal and “eyesclosed” biosignal with turning therapy on (e.g., initiating the deliveryof electrical stimulation). As other examples, the clinician mayassociate a particular pattern of the patient's “eyes open” biosignaland “eyes closed” biosignal with an increase or decrease in amplitude ofstimulation or a switch to another stimulation program.

FIG. 13 is a flow diagram illustrating an embodiment of a technique thatmay be employed by programmer 30 to correlate one or more biosignalswith a volitional patient thought related to a patient activity. Whilethe technique shown in FIG. 13 is primarily described with respect totherapy system 10, the technique may be employed with the other therapysystems described herein. Upon implantation of therapy system 10,biosignal detection module 66 of IMD 18 is programmed to detect relevantbiosignal and provide a signal to processor 60, which controls theadjustment of therapy indicated by the biosignal. The relevantbiosignals are determined via learning mode 146 of programmer 30.Patient 12 or the clinician may utilize the learning mode 146 ofprogrammer 30 at times other than the initial programming of biosignaldetection module 66, e.g., during the patient's follow-up visit to theclinician's office.

As shown in FIG. 13, the clinician accesses learning mode 146 ofprogrammer 30 (or another computing device) (160). Programmer 30 promptspatient 12 or the clinician to select an activity input from activityfield 148 and perform the selected activity (162). By performing theselected activity, patient 12 generates the volitional thoughts andprovides the volitional input that result in the detectable biosignalwithin brain 16. Biosignal detection module 66 of IMD 18 monitors theEEG signal within brain 16 that results from the volitional patientthought during the undertaking of the action. The clinician may thenextract the relevant biosignal from the EEG signal associated with thevolitional patient thought with the aid of processor 60 of IMD 18,processor 101 of programmer 30 or a processor of another device,

Programmer 30 may display activity field 148, which includes a pluralityof activities that patient 12 may undertake to generate the volitionalthought (164) and awaits the selection of another activity from activityfield 148 by patient 12 or the clinician (166). If programmer 30 doesnot receive the selection of activity inputs (166), programmer 30continues to display the list of activity inputs (164).

Once programmer 30 receives the activity input selection from patient 12(166), processor 60 of programmer 30 correlates the activity input withthe detected EEG signal (168). Processor 60 then stores the activity andassociated EEG signal in memory 62 (170). If the clinician desires tocontinue the learning mode (172), programmer again prompts patient 12 toselect another activity input (162). If the clinician does not desire tocontinue the learning mode (172), programmer 30 exits the learning modeand enters the normal operating mode of IMD 18 (174). In the normaloperating mode, IMD 18 may remain in a standby mode or deliver therapyaccording to a program until patient 12 creates the volitional cue thatgenerates a detectable biosignal for adjusting therapy.

FIG. 14 is a flow diagram of a technique for determining the biosignalthat indicates patient 12 generated a volitional thought indicative of adesired therapy adjustment. In the embodiment shown in FIG. 14, thebiosignal includes an EEG signal characteristic (in the time domain orfrequency domain). However, in other embodiments, the biosignal mayinclude other neural-based signals, such as deep brain electricalsignals. Factors that may affect the relevant EEG signal characteristicmay include factors such as the age, size, and relative health of thepatient. The relevant EEG signal characteristic may even vary for asingle patient, depending on fluctuating factors such as the state ofhydration, which may affect the fluid levels within the brain of thepatient. Accordingly, it may be desirable in some cases to measure theEEG signal of a particular patient over a finite trial period of timethat may be anywhere for less than one week to one or more months inorder to tune the trending data or threshold values of an EEG signalthat is associated with a particular volitional patient input to theparticular patient.

It is also believed that it is possible for the relevant EEG signalcharacteristic for a particular volitional patient input to be the samefor two or more patients. In such a case, one or more previouslydetermined EEG signal characteristic may be a starting point for aclinician, who may adapt (or “calibrate” or “tune”) the EEG signalcharacteristic value (e.g., a threshold amplitude or power value) to aparticular patient. The previously generated EEG signal characteristicvalue may be, for example, an average of threshold values for a largenumber (e.g., hundreds, or even thousands) of patients.

Processor 204 of biosignal detection module 200 monitors the EEG signalacquired by EEG sensing module 202 from the relevant region of brain 16of patient 12 (220). EEG sensing module 202 may acquire the EEG signalsubstantially continuously or at regular intervals, such as at afrequency of about 1 Hz to about 100 Hz. In addition, the EEG signal formore than one region of brain 16 may also be generated to determinewhich region of brain 16 provides the most relevant indication of thevolitional patient input. The region of brain 16 that provides the mostrelevant indication of the movement state may influence where electrodes212A-E are positioned.

During the same trial period of time, patient 12 is prompted to providethe input that is indicative of the desired therapy adjustment action(240). For example, in one embodiment, the volitional patient thoughtincludes moving an index finger in a particular pattern, and the patternof the index finger movement may be indicative of desired increase instimulation amplitude.

An EEG signal is associated with the volitional patient input (242). Inone embodiment, programmer 30 may provide an indication to biosignaldetection device 200 that patient 12 is generating the volitionalpatient thought, and processor 204 of biosignal detection device 200 mayassociate the EEG signal with the patient input. In another embodiment,biosignal detection module 200 may provide the monitored EEG signal toprogrammer 30, and processor 90 of programmer 30 may associate the EEGsignal with the patient input. The EEG signal may be matched to thevolitional patient thought any suitable way, e.g., based on the time ofoccurrence. For example, prior to, during or after the time in whichpatient 12 provide the volitional thought, patient 12 may depress abutton on programmer 30 to cause programmer 30 to record the date andtime, or alternatively, cause biosignal detection module 200 to recordthe date and time the volitional thought was executed.

Processor 204 of biosignal detection device 200, processor 90 ofprogrammer 30 or a processor of another computing device may record acharacteristic of the correlated EEG signal i.e., the biosignal, withinmemory (244). The biosignal may include the amplitude or a pattern inthe amplitude waveform of the EEG signal, the signal strength or apattern in the signal strength of the EEG signal within one or morefrequency bands, or other EEG signal characteristics. In one embodiment,a clinician or computing device may review the data relating to thevolitional patient input, and associate the EEG signal within a certaintime range prior to, e.g., 1 millisecond (ms) to about 3 seconds, andduring the volitional patient input. The clinician or computing devicemay compare the EEG signals for two or more times in which patient 12generates the volitional thought in order to confirm that the particularEEG signal characteristic, i.e., the biosignal, is indicative of adesired therapy adjustment action.

After correlating the EEG signal with a volitional patient thoughtindicative of a desired therapy adjustment action, the clinician mayrecord the EEG signal characteristic (244) for later use by processor204 of biosignal detection module 200, processor 90 of programmer 30 ora processor of a medical device. Alternatively, a computing device mayautomatically determine the relevant EEG signal characteristic.

FIG. 15 is a block diagram illustrating an exemplary frequency selectivesignal monitor 270 that includes a chopper-stabilized superheterodyneinstrumentation amplifier 272 and a signal analysis unit 273. Signalmonitor 270 may utilize a heterodyning, chopper-stabilized amplifierarchitecture to convert a selected frequency band of a physiologicalsignal to a baseband for analysis. The physiological signal may beanalyzed in one or more selected frequency bands to trigger delivery ofpatient therapy and/or recording of diagnostic information. In somecases, signal monitor 270 may be utilized within a medical device. Forexample, signal monitor 270 may be utilized within a biosignal detectionmodule included in IMD 18 implanted within patient 12 from FIG. 1. Inother cases, signal monitor 270 may be utilized within a separate sensorthat communicates with a medical device. For example, signal monitor 270may be utilized within biosignal detection module 39 implanted withinpatient 12 and coupled to IMD 36 from FIG. 2A or external cue device 54from FIG. 3. As another example, signal monitor 270 may be utilizedwithin biosignal detection module 42 positioned external to patient 12and coupled to IMD 36 from FIG. 2B or external cue device 54 from FIG.3.

In general, frequency selective signal monitor 270 provides aphysiological signal monitoring device comprising a physiologicalsensing element that receives a physiological signal, an instrumentationamplifier 272 comprising a modulator 282 that modulates the signal at afirst frequency, an amplifier that amplifies the modulated signal, and ademodulator 288 that demodulates the amplified signal at a secondfrequency different from the first frequency. A signal analysis unit 273that analyzes a characteristic of the signal in the selected frequencyband. The second frequency is selected such that the demodulatorsubstantially centers a selected frequency band of the signal at abaseband.

The signal analysis unit 273 may comprise a lowpass filter 274 thatfilters the demodulated signal to extract the selected frequency band ofthe signal at the baseband. The second frequency may differ from thefirst frequency by an offset that is approximately equal to a centerfrequency of the selected frequency band. In one embodiment, thephysiological signal is an electrical signal, such as an EEG signal,ECoG signal, EMG signal, field potential, and the selected frequencyband is one of an alpha, beta, gamma or high gamma frequency band of theelectrical signal. The characteristic of the demodulated signal is powerfluctuation of the signal in the selected frequency band. The signalanalysis unit 273 may generate a signal triggering at least one ofcontrol of therapy to the patient or recording of diagnostic informationwhen the power fluctuation exceeds a threshold.

In some embodiments, the selected frequency band comprises a firstselected frequency band and the characteristic comprises a first power.The demodulator 288 demodulates the amplified signal at a thirdfrequency different from the first and second frequencies. The thirdfrequency being selected such that the demodulator 288 substantiallycenters a second selected frequency band of the signal at a baseband.The signal analysis unit 273 analyzes a second power of the signal inthe second selected frequency band, and calculates a power ratio betweenthe first power and the second power. The signal analysis unit 273generates a signal triggering at least one of control of therapy to thepatient or recording of diagnostic information based on the power ratio.

In the example of FIG. 15, chopper-stabilized, superheterodyne amplifier272 modulates the physiological signal with a first carrier frequencyf_(c), amplifies the modulated signal, and demodulates the amplifiedsignal to baseband with a second frequency equivalent to the firstfrequency f_(c) plus (or minus) an offset δ. Signal analysis unit 273measures a characteristic of the demodulated signal in a selectedfrequency band.

The second frequency is different from the first frequency f_(c) and isselected, via the offset δ, to position the demodulated signal in theselected frequency band at the baseband. In particular, the offset maybe selected based on the selected frequency band. For example, thefrequency band may be a frequency within the selected frequency band,such as a center frequency of the band.

If the selected frequency band is 5 to 15 Hz, for example, the offset δmay be the center frequency of this band, i.e., 10 Hz. In someembodiments, the offset δ may be a frequency elsewhere in the selectedfrequency band. However, the center frequency generally will bepreferred. The second frequency may be generated by shifting the firstfrequency by the offset amount. Alternatively, the second frequency maybe generated independently of the first frequency such that thedifference between the first and second frequencies is the offset.

In either case, the second frequency may be equivalent to the firstfrequency f_(c) plus or minus the offset δ. If the first frequency f_(c)is 4000 Hz, for example, and the selected frequency band is 5 to 15 Hz(the alpha band for EEG signals), the offset δ may be selected as thecenter frequency of that band, i.e., 10 Hz. In this case, the secondfrequency is the first frequency of 4000 Hz plus or minus 10 Hz. Usingthe superheterodyne structure, the signal is modulated at 4000 Hz bymodulator 282, amplified by amplifier 286 and then demodulated bydemodulator 288 at 3990 or 4010 Hz (the first frequency f_(c) of 4000 Hzplus or minus the offset δ of 10 Hz) to position the 5 to 15 Hz bandcentered at 10 Hz at baseband, e.g., DC. In this manner the 5 to 15 Hzband can be directly downconverted such that it is substantiallycentered at DC.

As illustrated in FIG. 15, superheterodyne instrumentation amplifier 272receives a physiological signal (e.g., V_(in)) from sensing elementspositioned at a desired location within a patient or external to apatient to detect the physiological signal. For example, thephysiological signal may comprise one of an EEG, EcoG, electromyogramEMG, ECG, pressure, temperature, impedance or motion signal. Again, anEEG signal will be described for purposes of illustration.Superheterodyne instrumentation amplifier 272 may be configured toreceive the physiological signal (V_(in)) as either a differential orsignal-ended input. Superheterodyne instrumentation amplifier 272includes first modulator 282 for modulating the physiological signalfrom baseband at the carrier frequency (f_(c)). In the example of FIG.15, an input capacitance (C_(in)) 283 couples the output of firstmodulator 282 to feedback adder 284. Feedback adder 284 will bedescribed below in conjunction with the feedback paths.

Adder 285 represents the inclusion of a noise signal with the modulatedsignal. Adder 285 represents the addition of low frequency noise, butdoes not form an actual component of superheterodyne instrumentationamplifier 272. Adder 285 models the noise that comes intosuperheterodyne instrumentation amplifier 272 from non-ideal transistorcharacteristics. At adder 285, the original baseband components of thesignal are located at the carrier frequency f_(c). As an example, thebaseband components of the signal may have a frequency within a range of0 to approximately 1000 Hz and the carrier frequency f_(c) may beapproximately 4 kHz to approximately 10 kHz. The noise signal enters thesignal pathway, as represented by adder 285, to produce a noisymodulated signal. The noise signal may include 1/f noise, popcorn noise,offset, and any other external signals that may enter the signal pathwayat low (baseband) frequency. At adder 285, however, the originalbaseband components of the signal have already been chopped to a higherfrequency band, e.g., 4000 Hz, by first modulator 282. Thus, thelow-frequency noise signal is segregated from the original basebandcomponents of the signal.

Amplifier 286 receives the noisy modulated input signal from adder 285.Amplifier 286 amplifies the noisy modulated signal and outputs theamplified signal to a second modulator 288. Offset (δ) 287 may be tunedsuch that it is approximately equal to a frequency within the selectedfrequency band, and preferably the center frequency of the selectedfrequency band. The resulting modulation frequency (f_(c)±δ) used bydemodulator 288 is then different from the first carrier frequency f_(c)by the offset amount δ. In some cases, offset δ 287 may be manuallytuned according to the selected frequency band by a physician,technician, or the patient. In other cases, the offset δ 287 may bydynamically tuned to the selected frequency band in accordance withstored frequency band values. For example, different frequency bands maybe scanned by automatically or manually tuning the offset δ according tocenter frequencies of the desired bands. As an example, when monitoringa patient's intent to move, the selected frequency band may be the alphafrequency band (5 Hz to 15 Hz). In this case, the offset δ may beapproximately the center frequency of the alpha band, i.e., 10 Hz. Asanother example, when monitoring tremor, the selected frequency band maybe the beta frequency band (15 Hz-35 Hz). In this case, the offset δ maybe approximately the center frequency of the beta band, i.e., 25 Hz. Asanother example, when monitoring intent in the cortex, the selectedfrequency band may be the high gamma frequency band (150 Hz-200 Hz). Inthis case, the offset δ may be approximately the center frequency of thehigh gamma band, i.e., 175 Hz. When monitoring pre-seizure biomarkers inepilepsy, the selected frequency may be fast ripples (500 Hz), in whichcase the offset δ may be approximately 500 Hz. As another illustration,the selected frequency band passed by filter 234 may be the gamma band(30 Hz-80 Hz), in which case the offset δ may be tuned to approximatelythe center frequency of the gamma band, i.e., 55 Hz.

Hence, the signal in the selected frequency band may be produced byselecting the offset (δ) 287 such that the carrier frequency plus orminus the offset frequency (f_(c)±δ) is equal to a frequency within theselected frequency band, such as the center frequency of the selectedfrequency band. In each case, as explained above, the offset may beselected to correspond to the desired band. For example, an offset of 5Hz would place the alpha band at the baseband frequency, e.g., DC, upondownconversion by the demodulator. Similarly, an offset of 15 Hz wouldplace the beta band at DC upon downconversion, and an offset of 30 Hzwould place the gamma band at DC upon downconversion. In this manner,the pertinent frequency band is centered at the baseband. Then, passivelow pass filtering may be applied to select the frequency band. In thismanner, the superheterodyne architecture serves to position the desiredfrequency band at baseband as a function of the selected offsetfrequency used to produce the second frequency for demodulation. Ingeneral, in the example of FIG. 15, powered bandpass filtering is notrequired. Likewise, the selected frequency band can be obtained withoutthe need for oversampling and digitization of the wideband signal.

With further reference to FIG. 15, second modulator 288 demodulates theamplified signal at the second frequency f_(c)±δ, which is separatedfrom the carrier frequency f_(c) by the offset δ. That is, secondmodulator 288 modulates the noise signal up to the f_(c)±δ frequency anddemodulates the components of the signal in the selected frequency banddirectly to baseband. Integrator 289 operates on the demodulated signalto pass the components of the signal in the selected frequency bandpositioned at baseband and substantially eliminate the components of thenoise signal at higher frequencies. In this manner, integrator 289provides compensation and filtering to the amplified signal to producean output signal (V_(out)). In other embodiments, compensation andfiltering may be provided by other circuitry.

As shown in FIG. 15, superheterodyne instrumentation amplifier 272 mayinclude two negative feedback paths to feedback adder 284 to reduceglitching in the output signal (V_(out)). In particular, the firstfeedback path includes a third modulator 290, which modulates the outputsignal at the carrier frequency plus or minus the offset δ, and afeedback capacitance (C_(fb)) 291 that is selected to produce desiredgain given the value of the input capacitance (C_(in)) 283. The firstfeedback path produces a feedback signal that is added to the originalmodulated signal at feedback adder 284 to produce attenuation andthereby generate gain at the output of amplifier 286.

The second feedback path may be optional, and may include an integrator292, a fourth modulator 293, which modulates the output signal at thecarrier frequency plus or minus the offset δ, and high pass filtercapacitance (C_(hp)) 294. Integrator 292 integrates the output signaland modulator 293 modulates the output of integrator 292 at the carrierfrequency. High pass filter capacitance (C_(hp)) 294 is selected tosubstantially eliminate components of the signal that have a frequencybelow the corner frequency of the high pass filter. For example, thesecond feedback path may set a corner frequency of approximately equalto 2.5 Hz, 0.5 Hz, or 0.05 Hz. The second feedback path produces afeedback signal that is added to the original modulated signal atfeedback adder 284 to increase input impedance at the output ofamplifier 286.

As described above, chopper-stabilized, superheterodyne instrumentationamplifier 272 can be used to achieve direct downconversion of a selectedfrequency band centered at a frequency that is offset from baseband byan amount δ. Again, if the alpha band is centered at 10 Hz, then theoffset amount δ used to produce the demodulation frequency f_(c)±δ maybe 10 Hz. As illustrated in FIG. 15, first modulator 282 is run at thecarrier frequency (f_(c)), which is specified by the 1/f corner andother constraints, while second modulator 288 is run at the selectedfrequency band (f_(c)±δ). Multiplication of the physiological signal bythe carrier frequency convolves the signal in the frequency domain. Thenet effect of upmodulation is to place the signal at the carrierfrequency (f_(c)). By then running second modulator 288 at a differentfrequency (f_(c)±δ), the convolution of the signal sends the signal inthe selected frequency band to baseband and 2δ. Integrator 289 may beprovided to filter out the 2δ component and passes the basebandcomponent of the signal in the selected frequency band.

As illustrated in FIG. 15, signal analysis unit 273 receives the outputsignal from instrumentation amplifier. In the example of FIG. 15, signalanalysis unit 273 includes a passive lowpass filter 274, a powermeasurement module 276, a lowpass filter 277, a threshold tracker 278and a comparator 280. Passive lowpass filter 274 extracts the signal inthe selected frequency band positioned at baseband. For example, lowpassfilter 274 may be configured to reject frequencies above a desiredfrequency, thereby preserving the signal in the selected frequency band.Power measurement module 276 then measures power of the extractedsignal. In some cases, power measurement module 276 may extract the netpower in the desired band by full wave rectification. In other cases,power measurement module 276 may extract the net power in the desiredband by a squaring power calculation, which may be provided by asquaring power circuit. As the signal has sine and cosine phases,summing of the squares yields a net of 1 and the total power. Themeasured power is then filtered by lowpass filter 277 and applied tocomparator 280. Threshold tracker 278 tracks fluctuations in powermeasurements of the selected frequency band over a period of time inorder to generate a baseline power threshold of the selected frequencyband for the patient. Threshold tracker 278 applies the baseline powerthreshold to comparator 280 in response to receiving the measured powerfrom power measurement module 276.

Comparator 280 compares the measured power from lowpass filter 277 withthe baseline power threshold from threshold tracker 278. If the measuredpower is greater than the baseline power threshold, comparator 280 mayoutput a trigger signal to a processor of a medical device to controltherapy and/or recording of diagnostic information. If the measuredpower is equal to or less than the baseline power threshold, comparator280 outputs a power tracking measurement to threshold tracker 278, asindicated by the line from comparator 280 to threshold tracker 278.Threshold tracker 278 may include a median filter that creates thebaseline threshold level after filtering the power of the signal in theselected frequency band for several minutes. In this way, the measuredpower of the signal in the selected frequency band may be used by thethreshold tracker 278 to update and generate the baseline powerthreshold of the selected frequency band for the patient. Hence, thebaseline power threshold may be dynamically adjusted as the sensedsignal changes over time. A signal above or below the baseline powerthreshold may signify an event that may support generation of a triggersignal.

In some cases, frequency selective signal monitor 270 may be limited tomonitoring a single frequency band of the wide band physiological signalat any specific instant. Alternatively, frequency selective signalmonitor 270 may be capable of efficiently hopping frequency bands inorder to monitor the signal in a first frequency band, monitor thesignal in a second frequency band, and then determine whether to triggertherapy and/or diagnostic recording based on some combination of themonitored signals. For example, different frequency bands may bemonitored on an alternating basis to support signal analysis techniquesthat rely on comparison or processing of characteristics associated withmultiple frequency bands.

FIG. 16 is a block diagram illustrating a portion of an exemplarychopper-stabilized superheterodyne instrumentation amplifier 272A foruse within frequency selective signal monitor 270 from FIG. 15.Superheterodyne instrumentation amplifier 272A illustrated in FIG. 16may operate substantially similar to superheterodyne instrumentationamplifier 272 from FIG. 15. Superheterodyne instrumentation amplifier272A includes a first modulator 295, an amplifier 297, a frequencyoffset 298, a second modulator 299, and a lowpass filter 300. In someembodiments, lowpass filter 300 may be an integrator, such as integrator289 of FIG. 15. Adder 296 represents addition of noise to the choppedsignal. However, adder 296 does not form an actual component ofsuperheterodyne instrumentation amplifier 272A. Adder 296 models thenoise that comes into superheterodyne instrumentation amplifier 272Afrom non-ideal transistor characteristics.

Superheterodyne instrumentation amplifier 272A receives a physiologicalsignal (V_(in)) associated with a patient from sensing elements, such aselectrodes, positioned within or external to the patient to detect thephysiological signal. First modulator 295 modulates the signal frombaseband at the carrier frequency (f_(c)). A noise signal is added tothe modulated signal, as represented by adder 296. Amplifier 297amplifies the noisy modulated signal. Frequency offset 298 is tuned suchthat the carrier frequency plus or minus frequency offset 298 (f_(c)±δ)is equal to the selected frequency band. Hence, the offset δ may beselected to target a desired frequency band. Second modulator 299modulates the noisy amplified signal at offset frequency 98 from thecarrier frequency f_(c). In this way, the amplified signal in theselected frequency band is demodulated directly to baseband and thenoise signal is modulated to the selected frequency band.

Lowpass filter 300 may filter the majority of the modulated noise signalout of the demodulated signal and set the effective bandwidth of itspassband around the center frequency of the selected frequency band. Asillustrated in the detail associated with lowpass filter 300 in FIG. 16,a passband 303 of lowpass filter 300 may be positioned at a centerfrequency of the selected frequency band. In some cases, the offset δmay be equal to this center frequency. Lowpass filter 300 may then setthe effective bandwidth (BW/2) of the passband around the centerfrequency such that the passband encompasses the entire selectedfrequency band. In this way, lowpass filter 300 passes a signal 301positioned anywhere within the selected frequency band. For example, ifthe selected frequency band is 5 to 15 Hz, for example, the offset δ maybe the center frequency of this band, i.e., 10 Hz, and the effectivebandwidth may be half the full bandwidth of the selected frequency band,i.e., 5 Hz. In this case, lowpass filter 300 rejects or at leastattenuates signals above 5 Hz, thereby limiting the passband signal tothe alpha band, which is centered at 0 Hz as a result of thesuperheterodyne process. Hence, the center frequency of the selectedfrequency band can be specified with the offset δ, and the bandwidth BWof the passband can be obtained independently with the lowpass filter300, with BW/2 about each side of the center frequency.

Lowpass filter 300 then outputs a low-noise physiological signal(V_(out)). The low-noise physiological signal may then be input tosignal analysis unit 273 from FIG. 15. As described above, signalanalysis unit 273 may extract the signal in the selected frequency bandpositioned at baseband, measure power of the extracted signal, andcompare the measured power to a baseline power threshold of the selectedfrequency band to determine whether to trigger patient therapy.

FIGS. 17A-17D are graphs illustrating the frequency components of asignal at various stages within superheterodyne instrumentationamplifier 272A of FIG. 16. In particular, FIG. 17A illustrates thefrequency components in a selected frequency band within thephysiological signal received by frequency selective signal monitor 270.The frequency components of the physiological signal are represented byline 302 and located at offset δ from baseband in FIG. 17A.

FIG. 17B illustrates the frequency components of the noisy modulatedsignal produced by modulator 295 and amplifier 297. In FIG. 17B, theoriginal offset frequency components of the physiological signal havebeen up-modulated at carrier frequency f_(c) and are represented bylines 304 at the odd harmonics. The frequency components of the noisesignal added to the modulated signal are represented by dotted line 305.In FIG. 17B, the energy of the frequency components of the noise signalis located substantially at baseband and energy of the frequencycomponents of the desired signal is located at the carrier frequency(f_(c)) plus and minus frequency offset (δ) 298 and its odd harmonics.

FIG. 17C illustrates the frequency components of the demodulated signalproduced by demodulator 299. In particular, the frequency components ofthe demodulated signal are located at baseband and at twice thefrequency offset (26), represented by lines 306. The frequencycomponents of the noise signal are modulated and represented by dottedline 307. The frequency components of the noise signal are located atthe carrier frequency plus or minus the offset frequency (δ) 298 and itsodd harmonics in FIG. 17C. FIG. 17C also illustrates the effect oflowpass filter 300 that may be applied to the demodulated signal. Thepassband of lowpass filter 300 is represented by dashed line 308.

FIG. 17D is a graph that illustrates the frequency components of theoutput signal. In FIG. 17D, the frequency components of the outputsignal are represented by line 310 and the frequency components of thenoise signal are represented by dotted line 311. FIG. 17D illustratesthat lowpass filter 300 removes the frequency components of thedemodulated signal located at twice the offset frequency (26). In thisway, lowpass filter 300 positions the frequency components of the signalat the desired frequency band within the physiological signal atbaseband. In addition, lowpass filter 300 removes the frequencycomponents from the noise signal that were located outside of thepassband of lowpass filter 300 shown in FIG. 17C. The energy from thenoise signal is substantially eliminated from the output signal, or atleast substantially reduced relative to the original noise signal thatotherwise would be introduced.

FIG. 18 is a block diagram illustrating a portion of an exemplarychopper-stabilized superheterodyne instrumentation amplifier 272B within-phase and quadrature signal paths for use within frequency selectivesignal monitor 270 from FIG. 15. The in-phase and quadrature signalpaths substantially reduce phase sensitivity within superheterodyneinstrumentation amplifier 272B. Because the signal obtained from thepatient and the clocks used to produce the modulation frequencies areuncorrelated, the phase of the signal should be taken into account. Toaddress the phasing issue, two parallel heterodyning amplifiers may bedriven with in-phase (I) and quadrature (Q) clocks created with on-chipdistribution circuits. Net power extraction then can be achieved withsuperposition of the in-phase and quadrature signals.

An analog implementation may use an on-chip self-cascoded Gilbert mixerto calculate the sum of squares. Alternatively, a digital approach maytake advantage of the low bandwidth of the I and Q channels afterlowpass filtering, and digitize at that point in the signal chain fordigital power computation. Digital computation at the I/Q stage hasadvantages. For example, power extraction is more linear than a tanhfunction. In addition, digital computation simplifies offset calibrationto suppress distortion, and preserves the phase information forcross-channel coherence analysis. With either technique, a sum ofsquares in the two channels can eliminate the phase sensitivity betweenthe physiological signal and the modulation clock frequency. The poweroutput signal can lowpass filtered to the order of 1 Hz to track theessential dynamics of a desired biomarker.

Superheterodyne instrumentation amplifier 272B illustrated in FIG. 18may operate substantially similar to superheterodyne instrumentationamplifier 272 from FIG. 15. Superheterodyne instrumentation amplifier272B includes an in-phase (I) signal path with a first modulator 320, anamplifier 322, an in-phase frequency offset (δ) 323, a second modulator324, a lowpass filter 325, and a squaring unit 326. Adder 321 representsaddition of noise. Adder 321 models the noise from non-ideal transistorcharacteristics. Superheterodyne instrumentation amplifier 272B includesa quadrature phase (Q) signal path with a third modulator 328, an adder329, an amplifier 330, a quadrature frequency offset (δ) 331, a fourthmodulator 332, a lowpass filter 333, and a squaring unit 334. Adder 329represents addition of noise. Adder 329 models the noise from non-idealtransistor characteristics.

Superheterodyne instrumentation amplifier 272B receives a physiologicalsignal (V_(in)) associated with a patient from one or more sensingelements. The in-phase (I) signal path modulates the signal frombaseband at the carrier frequency (f_(c)), permits addition of a noisesignal to the modulated signal, and amplifies the noisy modulatedsignal. In-phase frequency offset 323 may be tuned such that it issubstantially equivalent to a center frequency of a selected frequencyband. For the alpha band (5 to 15 Hz), for example, the offset 323 maybe approximately 10 Hz. In this example, if the modulation carrierfrequency f_(c) applied by modulator 320 is 4000 Hz, then thedemodulation frequency f_(c)±δ may be 3990 Hz or 4010 Hz.

Second modulator 324 modulates the noisy amplified signal at a frequency(f_(c)±δ) offset from the carrier frequency f_(c) by the offset amountS. In this way, the amplified signal in the selected frequency band maybe demodulated directly to baseband and the noise signal may bemodulated up to the second frequency f_(c)±δ. The selected frequencyband of the physiological signal is then substantially centered atbaseband, e.g., DC. For the alpha band (5 to 15 Hz), for example, thecenter frequency of 10 Hz is centered at 0 Hz at baseband. Lowpassfilter 325 filters the majority of the modulated noise signal out of thedemodulated signal and outputs a low-noise physiological signal. Thelow-noise physiological signal may then be squared with squaring unit326 and input to adder 336. In some cases, squaring unit 326 maycomprise a self-cascoded Gilbert mixer. The output of squaring unit 126represents the spectral power of the in-phase signal.

In a similar fashion, the quadrature (Q) signal path modulates thesignal from baseband at the carrier frequency (f_(c)). However, thecarrier frequency applied by modulator 328 in the Q signal path is 90degrees out of phase with the carrier frequency applied by modulator 320in the I signal path. The Q signal path permits addition of a noisesignal to the modulated signal, as represented by adder 329, andamplifies the noisy modulated signal via amplifier 330. Again,quadrature offset frequency (δ) 331 may be tuned such it isapproximately equal to the center frequency of the selected frequencyband. As a result, the demodulation frequency applied to demodulator 332is (f_(c)±δ). In the quadrature signal path, however, an additionalphase shift of 90 degrees is added to the demodulation frequency fordemodulator 332. Hence, the demodulation frequency for demodulator 332,like demodulator 324, is f_(c)±δ. However, the demodulation frequencyfor demodulator 332 is phase shifted by 90 degrees relative to thedemodulation frequency for demodulator 324 of the in-phase signal path.

Fourth modulator 332 modulates the noisy amplified signal at thequadrature frequency 331 from the carrier frequency. In this way, theamplified signal in the selected frequency band is demodulated directlyto baseband and the noise signal is modulated at the demodulationfrequency f_(c)±δ. Lowpass filter 333 filters the majority of themodulated noise signal out of the demodulated signal and outputs alow-noise physiological signal. The low-noise physiological signal maythen be squared and input to adder 336. Like squaring unit 326, squaringunit 334 may comprise a self-cascoded Gilbert mixer. The output ofsquaring unit 334 represents the spectral power of the quadraturesignal.

Adder 336 combines the signals output from squaring unit 326 in thein-phase signal path and squaring unit 334 in the quadrature signalpath. The output of adder 336 may be input to a lowpass filter 337 thatgenerates a low-noise, phase-insensitive output signal (V_(out)). Asdescribed above, the signal may be input to signal analysis unit 273from FIG. 15. As described above, signal analysis unit 273 may extractthe signal in the selected frequency band positioned at baseband,measure power of the extracted signal, and compare the measured power toa baseline power threshold of the selected frequency band to determinewhether to trigger patient therapy. Alternatively, signal analysis unit273 may analyze other characteristics of the signal. The signal Vout maybe applied to the signal analysis unit 273 as an analog signal.Alternatively, an analog-to-digital converter (ADC) may be provided toconvert the signal Vout to a digital signal for application to signalanalysis unit 273. Hence, signal analysis unit 273 may include one ormore analog components, one or more digital components, or a combinationof analog and digital components.

FIG. 19 is a circuit diagram illustrating an example mixer amplifiercircuit 400 for use in superheterodyne instrumentation amplifier 272 ofFIG. 15. For example, circuit 400 represents an example of amplifier286, demodulator 288 and integrator 289 in FIG. 15. Although the exampleof FIG. 19 illustrates a differential input, circuit 400 may beconstructed with a single-ended input. Accordingly, circuit 400 of FIG.19 is provided for purposes of illustration, without limitation as toother embodiments. In FIG. 19, VDD and VSS indicate power and groundpotentials, respectively.

Mixer amplifier circuit 400 amplifies a noisy modulated input signal toproduce an amplified signal and demodulates the amplified signal. Mixeramplifier circuit 400 also substantially eliminates noise from thedemodulated signal to generate the output signal. In the example of FIG.19, mixer amplifier circuit 400 is a modified folded-cascode amplifierwith switching at low impedance nodes. The modified folded-cascodearchitecture allows currents to be partitioned to maximize noiseefficiency. In general, the folded cascode architecture is modified inFIG. 19 by adding two sets of switches. One set of switches isillustrated in FIG. 19 as switches 402A and 402B (collectively referredto as “switches 402”) and the other set of switches includes switches404A and 404B (collectively referred to as “switches 404”).

Switches 402 are driven by chop logic to support the chopping of theamplified signal for demodulation at the chop frequency. In particular,switches 402 demodulate the amplified signal and modulate front-endoffsets and 1/f noise. Switches 404 are embedded within a self-biasedcascode mirror formed by transistors M6, M7, M8 and M9, and are drivenby chop logic to up-modulate the low frequency errors from transistorsM8 and M9. Low frequency errors in transistors M6 and M7 are attenuatedby source degeneration from transistors M8 and M9. The output of mixeramplifier circuit 400 is at baseband, allowing an integrator formed bytransistor M10 and capacitor 406 (Ccomp) to stabilize a feedback path(not shown in FIG. 19) between the output and input and filter modulatedoffsets.

In the example of FIG. 19, mixer amplifier circuit 400 has three mainblocks: a transconductor, a demodulator, and an integrator. The core issimilar to a folded cascode. In the transconductor section, transistorM5 is a current source for the differential pair of input transistors M1and M2. In some embodiments, transistor M5 may pass approximately 800nA, which is split between transistors M1 and M2, e.g., 400 nA each.Transistors M1 and M2 are the inputs to amplifier 286. Small voltagedifferences steer differential current into the drains of transistors M1and M2 in a typical differential pair way. Transistors M3 and M4 serveas low side current sinks, and may each sink roughly 500 nA, which is afixed, generally nonvarying current. Transistors M1, M2, M3, M4 and M5together form a differential transconductor.

In this example, approximately 100 nA of current is pulled through eachleg of the demodulator section. The AC current at the chop frequencyfrom transistors M1 and M2 also flows through the legs of thedemodulator. Switches 402 alternate the current back and forth betweenthe legs of the demodulator to demodulate the measurement signal back tobaseband, while the offsets from the transconductor are up-modulated tothe chopper frequency. As discussed previously, transistors M6, M7, M8and M9 form a self-biased cascode mirror, and make the signalsingle-ended before passing into the output integrator formed bytransistor M10 and capacitor 406 (Ccomp). Switches 404 placed within thecascode (M6-M9) upmodulate the low frequency errors from transistors M8and M9, while the low frequency errors of transistor M6 and transistorM7 are suppressed by the source degeneration they see from transistorsM8 and M9. Source degeneration also keeps errors from Bias N2transistors 408 suppressed. Bias N2 transistors M12 and M13 form acommon gate amplifier that presents a low impedance to the chopperswitching and passes the signal current to transistors M6 and M7 withimmunity to the voltage on the drains.

The output DC signal current and the upmodulated error current pass tothe integrator, which is formed by transistor M10, capacitor 406, andthe bottom NFET current source transistor M11. Again, this integratorserves to both stabilize the feedback path and filter out theupmodulated error sources. The bias for transistor M10 may beapproximately 100 nA, and is scaled compared to transistor M8. The biasfor lowside NFET M11 may also be approximately 100 nA (sink). As aresult, the integrator is balanced with no signal. If more current driveis desired, current in the integration tail can be increasedappropriately using standard integrate circuit design techniques.Various transistors in the example of FIG. 19 may be field effecttransistors (FETs), and more particularly CMOS transistors.

FIG. 20 is a circuit diagram illustrating an instrumentation amplifier410 with differential inputs V_(in)+ and V_(in)−. Instrumentationamplifier 410 is an example embodiment of superheterodyneinstrumentation amplifier 272 previously described in this disclosurewith reference to FIG. 15. FIG. 20 uses several reference numerals fromFIG. 15 to refer to like components. However, the optional high passfilter feedback path comprising components 292, 293 and 294 is omittedfrom the example of FIG. 20. In general, instrumentation amplifier 410may be constructed as a single-ended or differentia amplifier. Theexample of FIG. 20 illustrates example circuitry for implementing adifferential amplifier. The circuitry of FIG. 20 may be configured foruse in each of the I and Q signal paths of FIG. 18.

In the example of FIG. 20, instrumentation amplifier 410 includes aninterface to one or more sensing elements that produce a differentialinput signal providing voltage signals V_(in)+, V_(in)−. Thedifferential input signal may be provided by a sensor comprising any ofa variety of sensing elements, such as a set of one or more electrodes,an accelerometer, a pressure sensor, a force sensor, a gyroscope, ahumidity sensor, a chemical sensor, or the like. For brain sensing, thedifferential signal V_(in)+, V_(in)− may be, for example, an EEG or EcoGsignal.

The differential input voltage signals are connected to respectivecapacitors 283A and 283B (collectively referred to as “capacitors 283”)through switches 412A and 412B, respectively. Switches 412A and 412B maycollectively form modulator 282 of FIG. 15. Switches 412A, 412B aredriven by a clock signal provided by a system clock (not shown) at thecarrier frequency f_(c). Switches 412A, 412B may be cross-coupled toeach other, as shown in FIG. 20, to reject common-mode signals.Capacitors 283 are coupled at one end to a corresponding one of switches412A, 412B and to a corresponding input of amplifier 286 at the otherend. In particular, capacitor 283A is coupled to the positive input ofamplifier 286, and capacitor 283B is coupled to the negative input ofamplifier 286, providing a differential input. Amplifier 286, modulator288 and integrator 289 together may form a mixer amplifier, which may beconstructed similar to mixer amplifier 400 of FIG. 19.

In FIG. 20, switches 412A, 412B and capacitors 283A, 283B form a frontend of instrumentation amplifier 410. In particular, the front end mayoperate as a continuous time switched capacitor network. Switches 412A,412B toggle between an open state and a closed state in which inputssignals V_(in)+, V_(in)− are coupled to capacitors 283A, 283B at a clockfrequency f_(c) to modulate (chop) the input signal to the carrier(clock) frequency. As mentioned previously, the input signal may be alow frequency signal within a range of approximately 0 Hz toapproximately 1000 Hz and, more particularly, approximately 0 Hz to 500Hz, and still more particularly less than or equal to approximately 100Hz. The carrier frequency may be within a range of approximately 4 kHzto approximately 10 kHz. Hence, the low frequency signal is chopped tothe higher chop frequency band.

Switches 412A, 412B toggle in-phase with one another to provide adifferential input signal to amplifier 286. During one phase of theclock signal f_(c), switch 412A connects Vin+ to capacitor 283A andswitch 412B connects Vin− to capacitor 283B. During another phase,switches 412A, 412B change state such that switch 412A decouples Vin+from capacitor 283A and switch 412B decouples Vin− from capacitor 283B.Switches 412A, 412B synchronously alternate between the first and secondphases to modulate the differential voltage at the carrier frequency.The resulting chopped differential signal is applied across capacitors283A, 283B, which couple the differential signal across the positive andnegative inputs of amplifier 286.

Resistors 414A and 414B (collectively referred to as “resistors 414”)may be included to provide a DC conduction path that controls thevoltage bias at the input of amplifier 286. In other words, resistors414 may be selected to provide an equivalent resistance that is used tokeep the bias impedance high. Resistors 414 may, for example, beselected to provide a 5 GΩ equivalent resistor, but the absolute size ofthe equivalent resistor is not critical to the performance ofinstrumentation amplifier 410. In general, increasing the impedanceimproves the noise performance and rejection of harmonics, but extendsthe recovery time from an overload. To provide a frame of reference, a 5GΩ equivalent resistor results in a referred-to-input (RTI) noise ofapproximately 20 nV/rt Hz with an input capacitance (Cin) ofapproximately 25 pF. In light of this, a stronger motivation for keepingthe impedance high is the rejection of high frequency harmonics whichcan alias into the signal chain due to settling at the input nodes ofamplifier 286 during each half of a clock cycle.

Resistors 414 are merely exemplary and serve to illustrate one of manydifferent biasing schemes for controlling the signal input to amplifier286. In fact, the biasing scheme is flexible because the absolute valueof the resulting equivalent resistance is not critical. In general, thetime constant of resistor 414 and input capacitor 283 may be selected tobe approximately 100 times longer than the reciprocal of the choppingfrequency.

Amplifier 286 may produce noise and offset in the differential signalapplied to its inputs. For this reason, the differential input signal ischopped via switches 412A, 412B and capacitors 283A, 283B to place thesignal of interest in a different frequency band from the noise andoffset. Then, instrumentation amplifier 410 chops the amplified signalat modulator 88 a second time to demodulate the signal of interest downto baseband while modulating the noise and offset up to the chopfrequency band. In this manner, instrumentation amplifier 410 maintainssubstantial separation between the noise and offset and the signal ofinterest.

Modulator 288 may support direct downconversion of the selectedfrequency band using a superheterodyne process. In particular, modulator288 may demodulate the output of amplifier 86 at a frequency equal tothe carrier frequency f_(c) used by switches 412A, 412B plus or minus anoffset δ that is substantially equal to the center frequency of theselected frequency band. In other words, modulator 88 demodulates theamplified signal at a frequency of f_(c)±δ. Integrator 289 may beprovided to integrate the output of modulator 288 to produce outputsignal Vout. Amplifier 286 and differential feedback path branches 416A,416B process the noisy modulated input signal to achieve a stablemeasurement of the low frequency input signal output while operating atlow power.

Operating at low power tends to limit the bandwidth of amplifier 286 andcreates distortion (ripple) in the output signal. Amplifier 286,modulator 288, integrator 289 and feedback paths 416A, 416B maysubstantially eliminate dynamic limitations of chopper stabilizationthrough a combination of chopping at low-impedance nodes and ACfeedback, respectively.

In FIG. 20, amplifier 286, modulator 288 and integrator 289 arerepresented with appropriate circuit symbols in the interest ofsimplicity. However, it should be understood that such components may beimplemented in accordance with the circuit diagram of mixer amplifiercircuit 400 provided in FIG. 19. Instrumentation amplifier 410 mayprovide synchronous demodulation with respect to the input signal andsubstantially eliminate 1/f noise, popcorn noise, and offset from thesignal to output a signal that is an amplified representation of thedifferential voltage Vin+, Vin−.

Without the negative feedback provided by feedback path 416A, 416B, theoutput of amplifier 286, modulator 288 and integrator 289 could includespikes superimposed on the desired signal because of the limitedbandwidth of the amplifier at low power. However, the negative feedbackprovided by feedback path 416A, 416B suppresses these spikes so that theoutput of instrumentation amplifier 410 in steady state is an amplifiedrepresentation of the differential voltage produced across the inputs ofamplifier 286 with very little noise.

Feedback paths 416A, 216B, as shown in FIG. 20, include two feedbackpath branches that provide a differential-to-single ended interface.Amplifier 286, modulator 288 and integrator 289 may be referred tocollectively as a mixer amplifier. The top feedback path branch 416Amodulates the output of this mixer amplifier to provide negativefeedback to the positive input terminal of amplifier 286. The topfeedback path branch 416A includes capacitor 418A and switch 420A.Similarly, the bottom feedback path branch 416B includes capacitor 418Band switch 420B that modulate the output of the mixer amplifier toprovide negative feedback to the negative input terminal of the mixeramplifier. Capacitors 418A, 418B are connected at one end to switches420A, 420B, respectively, and at the other end to the positive andnegative input terminals of the mixer amplifier, respectively.Capacitors 418A, 418B may correspond to capacitor 291 in FIG. 15.Likewise, switches 420A, 420B may correspond to modulator 290 of FIG.15.

Switches 420A and 420B toggle between a reference voltage (Vref) and theoutput of the mixer amplifier 400 to place a charge on capacitors 418Aand 418B, respectively. The reference voltage may be, for example, amid-rail voltage between a maximum rail voltage of amplifier 286 andground. For example, if the amplifier circuit is powered with a sourceof 0 to 2 volts, then the mid-rail Vref voltage may be on the order of 1volt. Switches 420A and 420B should be 180 degrees out of phase witheach other to ensure that a negative feedback path exists during eachhalf of the clock cycle. One of switches 420A, 420B should also besynchronized with the mixer amplifier 400 so that the negative feedbacksuppresses the amplitude of the input signal to the mixer amplifier tokeep the signal change small in steady state. Hence, a first one of theswitches 420A, 420B may modulate at a frequency of f_(c)±δ, while asecond switch 420A, 420B modulates at a frequency of f_(c)±δ, but 180degrees out of phase with the first switch. By keeping the signal changesmall and switching at low impedance nodes of the mixer amplifier, e.g.,as shown in the circuit diagram of FIG. 19, the only significant voltagetransitions occur at switching nodes. Consequently, glitching (ripples)is substantially eliminated or reduced at the output of the mixeramplifier.

Switches 412 and 420, as well as the switches at low impedance nodes ofthe mixer amplifier, may be CMOS SPDT switches. CMOS switches providefast switching dynamics that enables switching to be viewed as acontinuous process. The transfer function of instrumentation amplifier210 may be defined by the transfer function provided in equation (1)below, where Vout is the voltage of the output of mixer amplifier 400,Cin is the capacitance of input capacitors 283, ΔVin is the differentialvoltage at the inputs to amplifier 286, Cfb is the capacitance offeedback capacitors 418A, 418B, and Vref is the reference voltage thatswitches 420A, 420B mix with the output of mixer amplifier 400.

Vout=Cin(ΔVin)/Cfb+Vref  (1)

From equation (1), it is clear that the gain of instrumentationamplifier 410 is set by the ratio of input capacitors Cin and feedbackcapacitors Cfb, i.e., capacitors 283 and capacitors 418. The ratio ofCin/Cfb may be selected to be on the order of 100. Capacitors 418 may bepoly-poly, on-chip capacitors or other types of MOS capacitors andshould be well matched, i.e., symmetrical.

Although not shown in FIG. 20, instrumentation amplifier 410 may includeshunt feedback paths for auto-zeroing amplifier 410. The shunt feedbackpaths may be used to quickly reset amplifier 410. An emergency rechargeswitch also may be provided to shunt the biasing node to help reset theamplifier quickly. The function of input capacitors 283 is toup-modulate the low-frequency differential voltage and rejectcommon-mode signals. As discussed above, to achieve up-modulation, thedifferential inputs are connected to sensing capacitors 283A, 283Bthrough SPDT switches 412A, 412B, respectively. The phasing of theswitches provides for a differential input to amplifier 286. Theseswitches 412A, 412B operate at the clock frequency, e.g., 4 kHz. Becausecapacitors 283A, 283B toggle between the two inputs, the differentialvoltage is up-modulated to the carrier frequency while the low-frequencycommon-mode signals are suppressed by a zero in the charge transferfunction. The rejection of higher-bandwidth common signals relies onthis differential architecture and good matching of the capacitors.

Blanking circuitry may be provided in some embodiments for applicationsin which measurements are taken in conjunction with stimulation pulsesdelivered by a cardiac pacemaker, cardiac defibrillator, orneurostimulator. Such blanking circuitry may be added between the inputsof amplifier 286 and coupling capacitors 283A, 283B to ensure that theinput signal settles before reconnecting amplifier 86 to the inputsignal. For example, the blanking circuitry may be a blankingmultiplexer (MUX) that selectively couples and decouples amplifier 286from the input signal. This blanking circuitry may selectively decouplethe amplifier 286 from the differential input signal and selectivelydisable the first and second modulators, i.e., switches 412, 420, e.g.,during delivery of a stimulation pulse.

A blanking MUX is optional but may be desirable. The clocks drivingswitches 412, 420 to function as modulators cannot be simply shut offbecause the residual offset voltage on the mixer amplifier wouldsaturate the amplifier in a few milliseconds. For this reason, ablanking MUX may be provided to decouple amplifier 86 from the inputsignal for a specified period of time during and following applicationof a stimulation by a cardiac pacemaker or defibrillator, or by aneurostimulator.

To achieve suitable blanking, the input and feedback switches 412, 420should be disabled while the mixer amplifier continues to demodulate theinput signal. This holds the state of integrator 289 within the mixeramplifier because the modulated signal is not present at the inputs ofthe integrator, while the demodulator continues to chop the DC offsets.Accordingly, a blanking MUX may further include circuitry or beassociated with circuitry configured to selectively disable switches412, 420 during a blanking interval. Post blanking, the mixer amplifiermay require additional time to resettle because some perturbations mayremain. Thus, the total blanking time includes time for demodulating theinput signal while the input switches 412, 420 are disabled and time forsettling of any remaining perturbations. An example blanking timefollowing application of a stimulation pulse may be approximately 8 mswith 5 ms for the mixer amplifier and 3 ms for the AC couplingcomponents.

Examples of various additional chopper amplifier circuits that may besuitable for or adapted to the techniques, circuits and devices of thisdisclosure are described in U.S. Pat. No. 7,385,443 to Timothy J.Denison, which is entitled “Chopper Stabilized InstrumentationAmplifier” and was issued on Jun. 10, 2008. The entire content of U.S.Pat. No. 7,385,443 is incorporated herein by reference.

Various embodiments of the described invention may include processorsthat are realized by microprocessors, ASICs, FPGA, or other equivalentintegrated logic circuitry. The processor may also utilize severaldifferent types of storage methods to hold computer-readableinstructions for the device operation and data storage. These memory andstorage media types may include a type of hard disk, RAM, or flashmemory, e.g. CompactFlash, SmartMedia, or Secure Digital (SD). Eachstorage option may be chosen depending on the embodiment of theinvention. While IMD 14 may contain permanent memory, externalprogrammer 20 may contain a more portable removable memory type toenable easy data transfer or offline data analysis.

Many embodiments of the disclosure have been described. Variousmodifications may be made without departing from the scope of theclaims. For example, while an EEG signal is used in many of the examplesherein to detect volitional patient input, in other embodiments, otherbioelectrical signals may also be useful. As other examples ofbioelectrical signals that may be indicative of volitional patientinput, an EMG signal may be used to detect specific muscle movement(e.g., eye winks, movement of a limb, etc.) or a specific pattern ofmuscle movement, or an ECoG signal that measures electrical signals on asurface of brain 16 may also indicate a particular volitional patientinput. As another example, electrodes placed within the motor cortex orother regions of brain 16 may detect field potentials within theparticular region of the brain, and the field potential may beindicative of a particular patient input. The particular bioelectricalsignal that is indicative of the volitional patient input related to thetherapy adjustment may be determined during a trial stage, as describedabove with respect to the EEG signal.

In addition, a processor may employ any suitable signal processingtechnique to determine whether the bioelectrical signal includes thebiosignal. For example, as described above with respect to EEG signals,an EMG, ECoG or field potential signal may be analyzed for arelationship between a voltage or amplitude of the signal and athreshold value, temporal correlation or frequency correlation with atemplate signal, power levels within one or more frequency bands, ratiosof power levels within two or more frequency bands, or combinationsthereof.

These and other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A method comprising: receiving an electricalsignal sensed from a patient; receiving an indication of an inputindicative of a patient activity; associating at least one biosignalwith the input indicative of the patient activity, wherein the at leastone biosignal is based on the electrical signal; detecting, from thepatient, the at least one biosignal that results from a volitionalpatient input corresponding to the input indicative of the patientactivity; and controlling, by a processor and based on the detection ofthe at least one biosignal, adjustment of a parameter that at leastpartially defines therapy delivery to the patient.
 2. The method ofclaim 1, further comprising controlling a therapy module to delivertherapy to the patient according to at least the adjusted parameter. 3.The method of claim 1, wherein detecting the at least one biosignalcomprises detecting the at least one biosignal from a brain of thepatient.
 4. The method of claim 3, wherein the electrical signal is afirst electrical signal, and wherein the biosignal is extracted from asecond electrical signal comprising at least one of anelectroencephalogram (EEG) signal, electromyogram (EMG) signal,electrocorticogram (ECoG) signal or a field potential within the brainof the patient.
 5. The method of claim 1, wherein detecting the at leastone biosignal comprises detecting the at least one biosignal from one ormore muscles of the patient.
 6. The method of claim 1, wherein thebiosignal comprises at least one of a frequency component of theelectrical signal, an amplitude of the electrical signal, or a patternin an amplitude waveform of the electrical signal.
 7. The method ofclaim 1, wherein controlling the adjustment of the parameter comprisesadjusting the parameter of therapy by at least one of increasing ordecreasing a therapy parameter value, shifting between stored therapyprograms, or modifying a sensory cue.
 8. The method of claim 1, furthercomprising controlling a feedback mechanism to indicate that thebiosignal was detected.
 9. The method of claim 1, wherein associatingthe at least one biosignal with the input indicative of the patientactivity comprises associating, by an implantable medical device, the atleast one biosignal with the input indicative of the patient activity.10. The method of claim 1, wherein associating the at least onebiosignal with the input indicative of the patient activity comprisesassociating, by an external programmer, the at least one biosignal withthe input indicative of the patient activity.
 11. A system comprising: aprocessor configured to: receive an electrical signal sensed from apatient; receive an indication of an input indicative of a patientactivity; associate at least one biosignal with the input indicative ofthe patient activity, wherein the at least one biosignal is based on theelectrical signal; and a biosignal detection module configured todetect, from the patient, the at least one biosignal that results from avolitional patient input corresponding to the input indicative of thepatient activity; and a therapy module configured to deliver therapy tothe patient, wherein the therapy is at least partially defined by aparameter adjusted based on the detection of the at least one biosignal.12. The system of claim 11, wherein the biosignal detection module isconfigured to detect the at least one biosignal from a brain of thepatient.
 13. The system of claim 12, wherein the electrical signal is afirst electrical signal, and wherein the biosignal detection module isconfigured to extract the biosignal from a second electrical signalcomprising at least one of an electroencephalogram (EEG) signal,electromyogram (EMG) signal, electrocorticogram (ECoG) signal or a fieldpotential within the brain of the patient.
 14. The system of claim 11,wherein the biosignal detection module is configured to detect the atleast one biosignal from one or more muscles of the patient.
 15. Thesystem of claim 11, wherein the biosignal comprises at least one of afrequency component of the electrical signal, an amplitude of theelectrical signal, or a pattern in an amplitude waveform of theelectrical signal.
 16. The system of claim 11, further comprising afeedback mechanism separate from the therapy module, wherein theprocessor is configured to control the feedback mechanism to indicatethat the biosignal was detected.
 17. The system of claim 11, furthercomprising an implantable medical device that comprises the processor,and wherein the processor is configured to control, based on thedetection of the at least one biosignal, adjustment of the parameterthat at least partially defines therapy delivered by the therapy module.18. The system of claim 11, wherein the processor is a first processor,and wherein the system further comprises: an external programmer thatcomprises the first processor; and an implantable medical devicecomprising a second processor configured to control, based on thedetection of the at least one biosignal, adjustment of the parameterthat at least partially defines therapy delivered by the therapy module.19. A computer-readable storage medium comprising one or moreinstructions that, when executed, cause one or more processors to:receive an electrical signal sensed from a patient; receive anindication of an input indicative of a patient activity; associate atleast one biosignal with the input indicative of the patient activity,wherein the at least one biosignal is based on the electrical signal;detect, from the patient, the at least one biosignal that results from avolitional patient input corresponding to the input indicative of thepatient activity; and control, based on the detection of the at leastone biosignal, adjustment of a parameter that at least partially definestherapy delivered to the patient.
 20. The computer-readable storagemedium of claim 19, further comprising instructions that cause the oneor more processors to control a feedback mechanism to indicate that thebiosignal was detected.